Submitting a comment generates a 404 error.

Upgrading to 3.1.1 did not help. Any ideas folks?

Have you tried:

– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the Twenty Ten theme to rule out any theme-specific problems.

– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.

– re-uploading the wp-admin and wp-includes folders from a fresh download of WordPress.

– Deactivated all plugins – no change.
– Switched themes to Twenty Ten – no change.
– Reset the plugins folder – no change.
– Upgraded to 3.1.1, which involved deleting wp-admin and wp-includes before uploading new files. – no change.

You need to carry out all of the steps – one after the other.

Did that. Nothing.

Site url?

https://thecastle.paulmcelligott.com/

Do you have the url for a post where the comments are still open?

https://thecastle.paulmcelligott.com/2011/04/this-is-a-temporary-post/

Try resetting your custom permalinks back to the default setting. If this works, then set your custom permalink structure back up again and re-test.

Failing that, try:
– deactivating all plugins to see if this resolves the problem. If this works, re-activate the plugins one by one until you find the problematic plugin(s).

– switching to the Twenty Ten theme to rule out any theme-specific problems.

The form url looks OK – which suggests that something else is causing the 404 problem.

If I reset my permalinks to default, I don’t even get my 404 page. I get the browser’s “broken link” screen.

I’ve already done the stuff with plugins and theme.

Then there’s something happening at the server level that’s redirecting your urls. Do you have anything else running in the root domain?

There’s nothing at the domain root. And I have another WP 3.1 install at the same level (another sub-domain of paulmcelligott.com), on the same host, where the comments work fine.

OK – this is officially weird. Do you have an existing .htaccess file in the WP folder of this (problem) site? If so, can you try renaming it to something like .htaccess.old, resetting the permalinks back to the default and switching to Twenty Ten?

Also when you said you did the plugin thing, did you try resetting the plugins folder by FTP or PhpMyAdmin? Preferably by the latter method. Sometimes, an apparently inactive plugin can still cause problems.