[Rocksolid Theme Assistant] 406 Error on Save / Save and Close

Hi,

I installed the Rocksolid Theme Assistant for the Opensauce Theme, however I get this error page each time I try to save, I was wondering if anyone knows why this happens, and if so, would be able to tell me how I can stop it from happening? Below is the exact error,

Code:

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Not Acceptable

An appropriate representation of the requested resource /contao/main.php could not be found on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request

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Never seen that before, I think it may be some kind of compatibility with the script, I am a new user to Contao, having from Joomla. So I'm new to Contao but really like it so far and would like to continue using it.

Any help will be greatly appreciated!