Notifications that can't be acknowledged

Hi,

I've had a notification in my inbox here for a couple of months that won't go away when I hit "Acknowledge this list of notifications". I just get the following error message:

Array ( [error] => Validation error [code] => 2003 [errors] => Array ( => form_error_messages.source_type.default ) )

I had hoped that getting another notification might help to clear it, but now I've just got 2 notifications sitting there! Anything that can be done...?