Cant delete a calendar item

for some strange reason when i try to delete one particular calendar item i can't delete it, the item is grayed out.  If i click edit item I get an error  "Item does not  exist.  It may have been deleted by another user."  I have tried using the powershell outlined in this blog post (http://blog.fpweb.net/fun-with-powershell/) but i'm still getting the error:

>>
Exception calling "Delete" with "0" argument(s): "Item does not exist.
The page you selected contains an item that does not exist.  It may have been d
eleted by another user."
At line:5 char:15
+ $Zombie.Delete <<<< ()
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : DotNetMethodException

does anyone have any ideas?

thanks

kevin

krd