Windows Backup fails with 0x81000037? Check your filesystem

600 words, estimated reading time: 3 minute(s)
Originally published on August 17, 2023
Last modified on September 16, 2023

The Problem

Yesterday, in preparation for a “downgrade” to Windows 10 from 11, I was trying to make a backup of my Windows files (using the Windows 7 Backup and Restore control panel). Not long after it actually started copying the files, it spat out this error:

Windows Backup failed while trying to read from the shadow copy on one of the volumes being backed up. Please check in the event logs for any relevant errors.

The error code listed was 0x81000037, and the first thing I did out of instinct was look this code up. The official Microsoft support topic stated that this error is caused if a reparse point (Windows slang for symlink) points to a FAT volume or is located on a volume containing compressed files. The listed workaround for this error is to delete the offending reparse point, and to locate it the topic suggests using the command dir /al /s, which is roughly equivalent to find -type l in Unix-like systems.

The first roadblock occurred when I found out that there is no offending reparse point which could cause this error, so I consulted eventvwr and found out that Windows Backup leaves some logs at %WINDIR%\Logs\WindowsBackup. It seemed to me that there are certain cache files that caused it to fail, so I deleted them and tried again. The backup again failed and I tried doing this a few more times, but as nothing helped I eventually gave up.

The Solution

Having been unable to fix Windows’ backup utility, I decided to just copy the files to the backup drive and copy them over back after the “downgrade”. This is when the actual solution to my problem becomes visible: Windows Explorer errored, I forgot the exact message by now but it went something like “The file XYZ is not available at the location” or something, searching for the exact message is as pointless as always.

This usually indicates filesystem errors, so I ran chkdsk C: and, unsurprisingly, it found errors on the filesystem. Besides others, it mentions the files XYZ that couldn’t be copied to the backup drive. I ran chkdsk /scan C:, rebooted through the filesystem error notification that popped up right after (chkdsk /f C: and reboot will work as well) and let it fix the errors. Once it rebooted, the backup completed without errors. After installing Windows 10, restoring the backup was a breeze (I only had AppData to back up, everything else was already on other drives) and so I was quickly up and running, then amazed by how fast and snappy Windows 10 is compared to its “successor”, but that’s worthy of a separate post.

(I don’t expect to get around to writing such post anytime soon though.)

“Why are you writing about this?”

As you may know, Microsoft stuff is notorious for being not very well documented and it’s entirely possible (even if very unlikely) that someone else encounters the same issue I have and is left helpless thanks to Windows’ lack of a proper, easy-to-use, centralized and well-written technical documentation system (think of man’s sections 4, 5, 7 and 8 for an idea of what I mean), not to mention countless YouTubers that parrot the same solutions as mentioned on the web many times before. I hope that this article will be useful to the one or so person with the same issue that may stumble upon it.

TLDR: Nobody seems to have mentioned this before (please correct me if I’m wrong), so might as well help the potential other person stuck in the same boat as me.