Using kleopatra 2.2.0 on windows 7, if i certify a key with a non-exportable
certification, and then go to certify it again with a public certification, the
second certification fails with the unhelpful message "General Error".

I can work around this from the command line with "gpg --edit-key $keyid" and
then the delsig subcommand, but most people who want to use a key management GUI
like kleopatra are not going to want to do that. This makes kleopatra
significantly less useful.

The common use case is likely to be that the user accepts initial default choice
the first time they sign a key (which is to make a non-exportable
certification), and then to go back later when they realize they want their
certs to be public, and re-sign it.