For the past few weeks, I've been having issues with one computer where the DAT update may take 2 or 3 tries to pass.
Win2K, 8.5ip5. I had a bout of a similar issue a year or so ago, but it had been very reliable until last month. Basically, the failure is when it gets to 'Copying DAT', it fails after about 4-5 seconds. Normally, it takes about 15-20 seconds to copy. Nothing obvious in any of the logs.