account problem with calendar

VISTA home premium
what I did: changed name of my machine from walraven-pc to desktop
problem:

No longer get reminders from windows calendar

In task scheduler Library
Microsoft
Windows
WindowsCalendar
I get ' An error occurred for task Reminders - Walraven. Error message: The
specified account name is not valid',

OK that seems reasonable as I had to change several other schedules from
walraven-pc/walraven to desktop/walraven

however in this case the list of tasks is blank. Refresh results in repeat
of the error message.
Tried to delete the folder 'windowscalendar' says cannot delete. 'You must
delete all tasks from he folder before the folder can be deleted' - to tasks
listed to be deleted.

I seem to be in a catch 22 here.

Any help most appreciated.
Michael