WordPress MU

I installed Wordpress Mu 2.7 on a dedicated Cpanel LAMP server, and it was working well. I then installed the SimplePie plugins, again, no problems. I then installed WP-O-Matic plugin, and configured it - no problems according to plugin, although I do NOT have multithreading set to on in PHP. When I started to add feeds to WP-O-Matic the main site crashes with: "Catchable fatal error: Object of class WP_Error could not be converted to string in /home/combatsp/public_html/wp-includes/comment.php on line 1264"
I cannot log into the main site, nor call it up - http://www.combatsportsreport.com.
The child accounts (subdomains) still seem to be running ok, but I can't delete plugins from them.
What can I do to repair this? Help would be very much appreciated.

you want to remove WP-O-Matic, then you should be able to log into your cpanel and still navigate the files and just delete the plugin.

or find the error on line 1264 in the file and fix it or comment it out for now to get past it.

Thanks for responding so quickly. Not knowing php, I don't want to make a bad situation worse by monkeying with the file...
How do I manually remove a plugin without wrecking the child accounts?

is this an mu-plugin? in otherwords did you put it in the mu-plugins folder or just the plugins folder

PHP doesn't actually support multi-threading but it does support forking.

There is no reference to WP_Error as a class anywhere round 1264 but that part of the code seems to handle pingbacks.

So try removing the Pingomatic plugin and see if things start working.

To remove a plugin if you cannot get to the back end you need to remove the source file/files from which ever plugin directory you put it in

Many thanks, and I truly appreciate your advice and assistance!
I removed the plugin via SSH and I appear to have regained control of the site.