Can't access Plugins Editor, gives 406 error

Yesterday, I noticed that when I try to access the Plugins Editor, I get a:

“406 error – Not Acceptable

An error has occurred. Generally a 406 error is caused because a request has been blocked by Mod Security. If you believe that your request has been blocked by mistake please contact the web site owner.”

What does this mean – I haven’t made any changes to the site, except upgraded plugins and such. I’ve tried de-activating all plugins, changed Themes and everything. Nothing works.

I don’t know much about mod security, but read that it’s there to protect my site, so I don’t want to leave my site unprotected. But I need to access the Editor.

Anybody, any thought?

Thanks!