MySQL Dump fails!

[sagelike]

I get this persistent error in my Application Logs:

BackupDiskFile::CreateMedia: Backup device 'C:\Program Files\SWsoft\Plesk\MySQL\Backup\psa-20080418.dump' failed to create. Operating system error 5(Access is denied.).

I tried changing permissions on that directory, giving full control to psaadm but that hasn't worked.

Has anyone run into this problem and how do I fix it?

thanks
G