Hi folks, We're running Small Business Server 2003 here. I was reviewing our backup procedures lately and noticed in the ntbackup logs that the differential backups of Exchange were failing with the error: (SERVERNAME)\Microsoft Information Store\First Storage Group is not a valid drive, or you do not have access. A quick search of google found this MS KB article: http://support.microsoft.com/kb/555613 However, both of the suggested fixes don't to apply to our problem. First solution is to make sure the backup media is formatted and has adequate space. Well, our backup target is a 1 TB external hard drive with about 600 gigs of free space. (A full backup of our Exchange DB is currently around 5 GB) The second suggested fix is to "perform a full backup before trying to do incremental". And again, that can't it because we are doing full backups twice a week. There are no errors in the application log, just entries for ntbackup starting and ending. I've also tested doing an differential & incremental backup onto the server's internal drive, which unsurprising still did not work. I could get around this problem by always doing a full backup of Exchange but I kind of like the idea of being space efficient with doing differential backups. Anyone got any ideas?