OS X :: Entourage Error Message - Could Not Read RGE File

Within the last week, all of our computers have developed a 'bouncing E'! The entourage symbol jumps up and down and demands attention, there is a box saying 'Entourage could not read this .rge file', it never stops, it just comes back every half hour or so. I suspect it has something to do with sharing projects, but we have done nothing differently from normal so can't trace the reason. It's possibly linked to when one person sent an invite to all the others asking them to attend and event but I'm not sure.

It was also suggested it might be because there is a lot (ie up to 10 years in one case!) of email in the in box, but we have been doing some clearing out with no result. I don't know much about macs and am in the dark here, and everyone is blaming me as it was my idea to create a shared diary/contacts list in entourage. Some other forum said to find the corrupted file, but I've no idea where to look or even how to tell that it's corrupt.