Outlook problem!?

It is happening with a couple of my users recently. The inbox in Outlook 2000 indicates that there are e.g. 90 messages in the Inbox, in fact there is a different number in there e.g. 17. I have tried to use the Inbox Repair Tool, but no result. Cananyone suggest anything else !? This has happened on W2K pro and WinNT4 wks.
Thank you