-snip-
That GitHub seems to confirm it's an issue with the wallet being on a different drive. Hopefully moving it to the main drive as I suggested will work.
Thanks, but I'm not sure how to use the walletdir option. How do I do that?
Either add
walletdir=PATH to your bitcoin.conf file, or launch bitcoin with the added command line or shortcut option
-walletdir=PATH, with PATH changed to a path to a directory on your main drive. If you say what OS you are using I can be more specific.