error with backing up

hi, hopefully someone bright is able to help me out here ??

Im experiencing a major problem with backing up my database.

As filosofo suggested in his forum, I changed the wp_db_backup.php to see whether that helped, but unfortunately also to no effect.

I have installed according to instructions, all permissions are correct, etc., etc.

And every time I receive the same message when clciking “backup!”
You are not allowed to perform backups.

Anyone? Please?

Thanks in advance!
Piet

(screen-shot of the error page)