I got this error message when I ran Switch to Classic Press
We have detected one or more incompatible plugins that prevent migrating your site to ClassicPress.
Please deactivate the following plugins if you wish to continue migrating your site to ClassicPress:
Yoast Duplicate Post, MetaSlider, Fixed Widget, Simple Lightbox, TablePress, Termly | GDPR/CCPA Cookie Consent Banner, Web Stories, Yoast SEO, WP Simple Paypal Shopping cart, Smush, Schema Glue for Yoast & The Events Calendar by WP Munich
Most of these are integral to the website
What can I do?
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Exactly what it says 
Please deactivate the following plugins if you wish to continue migrating your site to ClassicPress:
If you keep them active, there might be all sorts of issues from none, to PHP fatal errors, if switching to ClassicPress
You could test on a “testing Site” that uses ClassicPress if any of those plugins keep working on ClassicPress in order to have some time for finding substitutes.
However since their minimal required WordPress version in all cases will be above 5.0, it is very likely that none of those plugins will work fine with ClassicPress, which is why the plugin flags them and asks you to disable those prior to migration
There are a number of solutions you can try to substitute your current plugins, but not all.
Let me find the post we have that marks a few plugins that you might be interested in…
Edit:
This list of plugins will show what you can use instead of those you are using currently.
Be aware that the best would be to use Plugins made specifically for ClassicPress which you can find in the https://directory.classicpress.net directory - however probably you will not find substitutes for what you had active there, at this moment, in said directory, as it is still in the “early days” for it.
- For SEO you might want to look into classic seo: Classic SEO - ClassicPress Directory
- For calendars you could look into https://simplecalendar.io/
- For all other plugins I do not know any substitute out of the box, but the above linked list could have more solutions, and other members of the Community here could suggest other things
PS:
Can you confirm that with MetaSlider plugin you mean Slider, Gallery, and Carousel by MetaSlider – Responsive WordPress Slideshows – WordPress plugin | WordPress.org?
That plugin should not be flagged as incompatible since it supports WP below 4.9
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Thanks for the prompt reply
I am doing this in development area
I can confirm Slider, Gallery, and Carousel by MetaSlider – Responsive WordPress Plugin
I gather that I should deactivate all the plugins listed and then try to reactivate them and see if they work in CP, or do you have a list of known unusable plugins?
It would not be feasible to replace some of these plugins, so I would have to persevere with WordPress
If you are interested you can see the size and scope of the website here: https://ebps.org.uk/
I gather that I should deactivate all the plugins listed and then try to reactivate them and see if they work in CP, or do you have a list of known unusable plugins?
Everything that requires WordPress above 4.9.15 is technically to be assumed incompatible.
The migration plugin checks exactly that, and flags those telling you to disable them…
It might be that they (some of them) still work despite the requirement but it is unlikely.
Generally, all plugins that require WP 4.9.15 or below will work with ClassicPress, however it always should be put special attention when using WP Plugins on ClassicPress and if possible, substitute these with “real” ClassicPress plugins as far as available and possible. This is because WP Plugins can from one day to the other decide to “not work with WP 4.9.15 or below” anymore
I totally understand that many plugins cannot just be magically replaced, and in those cases of course one tries to keep using WP Plugins… but if they require WP above 4.9.15 the chances are very little those will work.
Sometimes you can add so called shims (see Providing Shims for functions introduced in or after WordPress 5.0 | ClassicPress Documentation) to make such plugins work with CP, but that is … more of a workaround than a solution and will not work in all cases.
So yes, trying to re-activate those plugins afterwards is an option but be prepared for errors, and eventually the need to find substitutes
I don’t understand why Slider, Gallery, and Carousel by MetaSlider – Responsive WordPress Plugin was flagged, it is not incompatible. Perhaps it is because of its minimal PHP version being below the one CP needs… I opened an issue in the repo of the migration plugin to analyse that.
The question is also if you need all these plugins.
For example, visiting the site I am not prompted for any cookie or GDPR agreements, yet you use Termly | GDPR/CCPA Cookie Consent Banner
It seems this could just be done with a simple page for the GDPR compliance, since I don’t have to agree to anything when the site when I visit it?
Perhaps you can take similar approaches with other of the plugins used (I am not familiar with the site, so I do not know where for example, or how often, you need sliders on the page, I couldn’t spot any on the first glimpse, but I am sure there are some 
)
Sometimes it is also relatively easy to create a tiny “must use” plugin, that does exactly what you need (lets say, a shortcode sliding thru a few images that you provide in attribute, or similar things)
I do not need all these plugins
I am trialling this on the dev site which is quite a bit out of date with the production site
I have deactivated all the plugins it has suggested and will try to reactivate them to see what happens
So I have done this and this is what I got
| Plugin | Works? | Required? |
|---|---|---|
| Fixed Widget | Y | |
| MetaSlider | ? | N |
| oik bwtrace | ? | N |
| Schema Glue for Yoast & The Events Calendar by WP Munich | N | |
| Simple Lightbox | Y | |
| Smush | N | |
| TablePress | N | |
| TablePress Extension: Responsive Tables | N | |
| TablePress Extension: Row Filtering | N | |
| Termly | GDPR/CCPA Cookie Consent Banner | ? |
| Uber Grid | Y | |
| Ultimate FAQs | Y | |
| VFB Pro | Y | |
| VFB Pro - Payments | Y | |
| Web Stories | N | |
| WP Downgrade | Specific Core Version | ? |
| WP Simple Paypal Shopping cart | Y | |
| WP Theme Tweaks | ? | N |
| WP User Avatars | ? | |
| Yoast Duplicate Post | N | |
| Yoast SEO | N |
If you can understand my table!
The important plugins that don’t work are
Tablepress (could I export all 200 as HTML and reimport them?)
Yoast SEO - you have an alternative for that
Smush - image compression - not vital
The Events Calendar - you have an alternative that looks good enough
Thanks for your help - I really do appreciate it
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Just to add some compatible alternatives for you to check out:
TablePress
- wpDataTables (WP 4.0+)
- Ninja Tables (WP 4.5+)
Smush
- ShortPixel (WP 4.2+) I use this one personally (including paid version) and it does optimize images better than Smush.
WP User Avatars
- Avatars (CP plugin)
Yoast Duplicate Post
- Carbon Copy (CP plugin)
Hope that helps. Do report any issue you’re seeing, so we can help.
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Thanks for the ideas
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I’m using the WP plugin reSmush.it for image compression. Works for me.
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You can check this out: ZP Cookie Notice. It’s made by one of the developers here, and it’s compatible with both WordPress and ClassicPress. I’m also using this.
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An update on the issue that MetaSlider was flagged as incompatible:
this is in fact a good thing, because while the main plugin declares compatibility with low WP versions, several of its bundled apps do require WP 5.+
This is visible in the nested readme files of said plugin.
This means, the Migration Plugin did a good job in flagging it. It shouldn’t be used on CP installs most likely it will or can break.
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Disappointing to see that TablePress in particular isn’t keeping WP 4.9 compatibility. It might be worth forking it on GitHub and doing our own release.
Yea, I checked version 1.14 the other day using wp-seek. There are only a few functions that require v5, and they do sound like general use functions CP might backport in the future.
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I asked Tobias if he could do something with TablePress and CP and the responswe was in the negative - see: https://wordpress.org/support/topic/classic-press/#post-14882750
Are you capable of forking it?
Is the error message that TablePress creaqtes substantive or can it be bypassed?
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In the future it’s best to ask plugin authors if they can continue to support WordPress 4.9. Then, no extra work is needed to support ClassicPress.
More info: Frequently Asked Questions | ClassicPress
Anyway, yes, since TablePress is open-source I have forked it to GitHub - ClassicPress-research/TablePress: TablePress is a plugin for WordPress. It enables you to create and manage tables on your website.. The easiest way forward is probably to roll back to an earlier version that was still compatible with WP 4.9 (and therefore ClassicPress).
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