Hi Robert,
The issue was not caused by the drive letter change. And it is as expected that change the drive letter back didn't fix the issue.
This issue is caused by some changes in Vault Add-in. It tries to resolve the file even when it is not checked into Vault, where Inventor itself can find the file from local disk successfully. I believe it is coincidence for you that all the files are library files which Inventor needs to re-locate.
This is a bug caused by Vault Add-in in Inventor 2010. We're very sorry about the inconvenience for you.
Given the workaround doesn't work for you, I guess maybe there are several files which need to be saved or some files are in library. Would you please try with the following step as well?
1. Click"Application Options" in the tools Ribbon.
2. Change to the "Save" page.
3. Check the box "Prompt to save for re-computable updates" and click "OK".
4. Open the file with this issue and click "Save" button. (If the file is in library, you will need to change the save to "Yes" manually, please refer to the attached image.)
This time, all the necessary files should be saved so that the prompt should not come out again.
Mandy Liu
Mandy Liu
Software Engineer
Manufacturing Industry Group
Autodesk, Inc.