Multiple error caused by unknow issue

[alfabet]

I'm currently experiencing multiple errors on my site, i think that they are all related in some way, for the reasons i'm going to explain, the issues are:

• removing an extension (mailchimp for magento) causes the backend and the frontend to get messy and unusable, i've tried, for what i know,to clean the cache and run the compilation process, but only restoring a backup solved the situation.
• Going in Payment methods > bank transfer payment > Istructions and changing in any way the text causes the frontend to get messy and the backend to be inaccessible. I've asked my server provider to know if there were problems with permissions. The permissions were setted right, he stated that he could see the link of the backend page changing, and that this was the problem, he has gived me this error from log. [access_compat:error] [...] AH01797: client denied by server configuration:

  Edit: I've actually found that the problem happens anywhere in configuration page.

Even if this errors seems disconnected (at least to me) I think they have a common source, because once i've copied the site to create a test environment i wasn't able to duplicate this issues. So, in my test site, copied from the same folders and with a copy of the same database, situaded in a subdomain in the same server, i can't get one of this errors.

Any one has any idea about what's going on? I'm kinda new to magento so i really don't know what to do. Many thanks.

[alfabet]

Anyone has any idea? Is really frustrating not being able to edit my configuration page.

Andrea.