I have seen this happening before on NT4 with shares set up. If you have marked the whole of the machine to be backed up, then Arcserve only backs things up once - even though the shares are listed as well as the drives and appear to be marked backed up again, Arcserve works out that this would be duplication. However, unmark just one of these items and Arcserve gets confused and backs things up twice. So, either mark the whole server to be backed up or just be specific and mark up the bits you need to be backed up.