Originally Posted by Sabardeyn
Alright. Suggestions on what to do next to identify and resolve the original error? Should I just send you a copy of the database without any formats attached? The metadata.db file is only 635 Kb. There are still two book entries that suffer from the error, so whatever is going on is still available for testing. (Even if I've gotten into the Edit Metadata for those two books, I've cancelled out to leave them available for testing.)
Got the metadata.db file. The problem is another manifestation of the bug I mentioned before. This time it was getting the empty string instead of "None", which caused the error.
The workaround is to fix the series index, which is most easily done by editing the cell directly on the spreadsheet and pressing return. The problem can exist if the GUI displays a (custom) series index of 1, but indices not equal 1 will have the problem.
I am submitting a fix to calibre that does this automatically when you edit metadata. It should be released on Friday.