Error codes

0x81000033

Backup failed: files could not be read

What it means

The backup engine could not read one or more files in the selected set, often because they were open or locked.

Common causes

• A file locked by another program
• Bad sectors on the source drive
• The backup target disconnected

How to fix it

1. Close apps that write constantly (databases, virtual machines, mail clients) and retry.
2. Check the source drive's health; back up the most important files first.
3. In services.msc make sure Volume Shadow Copy and Microsoft Software Shadow Copy Provider are running and set to Manual; then run vssadmin list writers and restart any writer that is not stable.
4. Try a file-based backup tool such as Duplicati for the files Windows Backup refuses.