Get a error in "Form Builder"

[Cogo]

Hi there.
When i try to change form layout in Form Builder and press save... ive got this messege:

Not Acceptable
An appropriate representation of the requested resource /admin/moduleinterface.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.

Everything else look like it works so i dont know what to do.
/ Cogo