Error message archiving project

Premiere Elements 2022 on windows 10. Trying to Archive a rather large project using the Copy option but the Archive errors out near the end (95%) of the copy with the error:

Premiere Elements has encountered an error.

[E:\adobe\pre\mezzanine\src\projectmanagerimpl.cpp-1816]

Odd error since the E:\ drive is my DVD drive.

16GB RAM and plenty of drive space on the BU drive as well as on the temporary files drives.

Archiving using Archive Project works fine.

I'm wondering if I have accidently deleted an asset that I'm not using but may still be in the Asset view. I scanned my assets but I don't know and couldn't find out what to look for an "orphaned" asset - one that is not longer where it was when I added it to assets.

Thanks for any advice you can give.