After installing web page not working

Hi after installing new cz version of WP I wanted isntall this booster. After activation I can not open my web page baubiologie.cz and elektrosmogmereni.cz.
So I have to change some files via ftp. But I dont know what.
THank you for help.
David

This is there:
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, admin@xhosting.cz and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

The page I need help with: [log in to see the link]