Hi Roger,
Sorry for my delay.
I have performed lots of research on this issue these days, I think you encounter the bug in Task scheduler that is described in the following article. This bug should have been fixed.
You can request and download the corresponding Vista SP1 hotfix via the following link, and try to install and apply on the problematic server. I have test on my side, it also applies on Windows Server 2008 and it can fix the issue.
The value in the Next Run Time field in Task Scheduler is incorrect on a Windows Vista-based computer
http://support.microsoft.com/kb/950035Please let me know if it fixes the issue on your machine.
Hope it helps.David Shen - MSFT
There is an amazing pack of free network admin tools.
click here to download it