Here something I noticed the other day. I'm doing a daily backup of my Outlook PST folder (see why here) when I hit this error: Code: Failed to backup file or folder 'C:\Documents and Settings\[user name]\Local Settings\Application Data\Microsoft\Outlook\archive.pst'. Error reading the file. (0x40001) Tag = 0x61F1883FE50B0A30 Snapshot read failed. (0x10C45A) Tag = 0x14181C22EF45AD23 The parameter is incorrect (0xFFF0) code = 80070057) Tag = 0xBD28FDBD64EDB8AF: Retry/Ignore/Cancel: User replied: Retry I inspected the folder being backed up and noticed that the file in question that was causing the error (archive.pst) had been compressed the last time I had run a Win XP Disk Cleanup. I opened the file properties dialog box for said file and unchecked "compress contents to save disk space". When I ran the backup again, it backed up without error. So, I'm wondering if anyone else has experienced errors when backing up files that have been compressed by Windows. I wonder if compressed files are to blame, at least in part, for the well documented ATI 11 stalling problems.