Hi Arthur,

Thank you for providing detailed information about the issue that occurred.

The backup fails because the file listed in the upgrade log is in use. This is not a bug in the wizard itself; we just report the error.

The mentioned file is part of the .vs folder, which Visual Studio uses to store information about the current state of the open solution. The file itself is auto-generated by Visual Studio for indexing, and we have no control over its usage. What the wizard does is to create a zip folder of the solution as backup, and this can not be done if there are file(s) in use or otherwise inaccessible. 

More about the .vs folder and the indexing file is available here:

c# - What is the .vs folder used for in Visual Studio solutions? - Stack Overflow

visual studio - How to disable that new "FileContentIndex" folder (and .vsidx files) in VS 2022 17.2.0? - Stack Overflow

As mentioned in the second article, you could try to disable the indexing and try upgrading again to produce the backup or alternatively, just archive the solution manually.

I hope that next time the upgrade process will be seamless.

Regards,
Nikola
Progress Telerik