error 0x80070005

I have been trying to set up daily backups as a scheduled task, but keep
getting this message: "An error has occurred while attempting to set task
account information. The specific error is: 0x80070005: Access is denied.
You do not have permission to perform the requested operation." I do have
full permissions so this should not be a problem. I have searched the
Microsoft Knowledge Base and there may be a hotfix that I could download that
might solve my problem, but I am cautioned that this hotfix must only be used
if I know for sure that my specific problem is the problem that this hotfix
is intended to fix. Has anyone else encountered this problem? And does
anyone have any suggestions how I could find out whether or not this hotfix
is the one I need? I would appreciate any help anyone could give me.
Thanks.