Outlook 98

When we are trying to delete emails from inbox, getting the following err message:

THIS ITEM COULD NOT BE DELETED. IT WAS EITHER MOVED OR DELETED OR ACCESS WAS DENIED.

THE MESSAGE INTERFACE HAS RETURNED AN UNKNOWN ERROR. IF THE PROBLEM PRESIST, RESTART OULTLOOK.

It is now happning with all the emails. with one or two. we have restarted outlook, but still getting the same error