[Xidos]

Encountered the exact same problem. In my case it was caused by the safety settings of my webhost. They disabled php scripts which had certain 'suspect' words in them. In my case 'home' wasn't allowed and while in 'edit templates' I would not be able to edit home.tpl, home_main.tpl etc. Instead I received the error notification above.

Solution in my case was to direct my host to alter the safety script by removing home as a suspect word.