Can not add sites

[movies111]

When try add a website (on example.com/?a=join) and click in "Add website", the screen goes blank.

What could be wrong?
You know if the owner of the script could help me?

 

[Basti]

Blank screen is usually a cause of a php fatal error.
So, please check your error log

My bet would be a plugin which adds something to the join form , but have not been installed.
Manually uploaded plugins via ftp you need to click install in admin -> plugins