Outlook 98

Hopefully someone can help with a very frustrating problem. We are running Outlook 98 and we have our inboxes grouped by From. The group headings are showing 11 items, 3 unread for instance, but you open the group and 11 items are not there, and no messages are unread, all seem to have been read. Also you cannot delete directly from this view. If you change views and delete then go back the number of items has not reduced, when it should have done. I have tried checking everything. This has happened over night literally on 2 PC's , the rest are fine. Can anyone shed some light please and if you have had the same problem and solved it??

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