comment preview?  is that a wp plugin?

we normally see 500 server errors on ajax responses when the file permissions are not correct…  so if you could verify that wp-content, plugins and simple-press directories are 0755 and the php files within simple press are 0644… depending on flavor of php could be slightly different but the key is not too restrictive and not 0777 which ajax has some problems with…

the other thing that can cause ajax some issues is mod_security… it has more false positive than true positives… are you running mod_security?

are your ajax issues on front end and admin? sorry, not sure what you were saying…

do you have link to your site so we can check for any other obvious js conflicts?

Nope, the Post Preview plugin for the forum.  I don’t really think it’s the plugin, just seemed to be a coincidence the problem happened at the same time.

I’ll try and explain the symptoms a little more clearly:

1. Enter the WordPress Dashboard
2. Click on the Forums item in the left menu
3. Forums page appears fine, shows the Manage Groups and Forums page
4. Click on Edit Group or Edit Forum on any of the items and the loading gif appears
5. However nothing actually happens
6. Check the Network tab in Google Chrome Dev tools and can see an AJAX call has taken place /index.php?sp_ahah=forums-loader but the response code is internal error 500, despite the actual response looking to be correct

Site was working fine up until I installed the Post Preview plugin, but as I seaid I believe that might be just a coincidence.  Will look into permissions now, everything should be setup as you’ve directed.

Link is http://www.fourtheye.net/f/

mod_security is installed, however disabling that made no difference to the problem.

the post preview plugin does not even load in the admin… weird… so probably not related…

but I can say base don the link provided you have some plugins or theme not following the wp api and standards… they are loading they own versions of jquery and jquery ui which could cause problems on the front end…

theme and plugin authors REALLY need to stop loading external libs like that when wp provides their own… no good reason to load external especially given that other theme and plugin others expect the wp versions… read more: http://codex.simple-press.com/codex/faq/troubleshooting/what-is-this-jquery-conflict/

your user messages plugin is also loading its own version of jquery autocomplete

this could also potentially conflict with the wp provided jquery autocomplete version… its much better to use the wp provided ones… cannot tell for sure, but it might be the user messages plugin also incorrectly loading the jquery and jquery ui…

or the theme… but it seems to be a twenty twelve child theme or derivative so unless it got messed up, it shouldnt be the one loading those js incorrectly…

but again, that’s front end… if problems are on admin side, not likely related…

Ok, seem to have solved the problem for now, though to be honest I’m not sure why this has fixed it.

Anyway, I’ve been using a WordPress plugin called Widget Logic for some time on the blog.  It’s always worked fine, even after the forum was installed yesterday.  However upon disabling that plugin (it was creating a whole bunch of lines in the error log) the AJAX inside the forum administration started working straight away.

And the Post Preview now works fine as well…

good news – sort of… not sure why it would be causing issues… is it current and up to date with wp 3.5?

Yep, the Widget Logic plug was up to date, and WP is at 3.5

Anyway, all good for now.  Thanks for the help.

glad we could help!