I recently upgraded two of my servers from 6.5.1 to 7.0 and all of the clients are still at 6.5.1. After the upgrade, a number of users started getting "Invalid or nonexistent document" when accessing certain documents. Now I now that most often the cause of this is that the user had deleted the document and they have a corrupt view. However, this is not the case. The users did not delete the documents, it is correspondence that they refer back to on a regular basis. When maintenence is run against the mail database, the documents are deleted. Unfortunately, I can't get them back because they all seem to be from a time period that I was not getting good backups. How can I stop this from happening and is it a result of the upgrade or just coincidence?