Our network has one elderly NT 3.50 workstation named LASER1 (running proprietary CNC software). I've long been running weekly backups of critical files on LASER1. On a nearby XP workstation, I map a drive (U to a network share on LASER1, then use XP's NTBackup. For six years it's run without any serious problems. Three weeks ago the XP workstation's backup log reported, "The network disk drive has stopped responding. Backup set aborted." The next week it did the same thing. Both times, the backup file was obviously much too small for the backup to have been successful. Last week, NTBackup instead logged messages like, "Could not access portions of file U100HOLES.CNC. You may not have permission to open the file, or the file may be missing or damaged," apparently for all 6000 files and directories on LASER1. However, the backup file size went back up to normal. Manually running the backup job today, I again got "Could not access portions" messages for everything, with a normal-sized backup file. A test restore apparently could retrieve all of the LASER1 files successfully; Windiff showed no differences between existing files on LASER1 and the test-restored files. But since the backup itself got errors, the verify step was never run. Connecting to LASER1 over the network, I can read any desired file normally. Any idea what's suddenly causing these errors, and how to get rid of them? NT 3.50 on LASER1 never gets updated; the XP workstation running NTBackup had the April Microsoft security updates installed the morning before the first backup failed. Thanks!