I'm using PGP Desktop (10.0.0) to sign text in the clipboard, but not all of my private keys show up in the drop-down list of signing keys. It's particularly frustrating because the key I want to use is the oldest (original) key I have, and it's usually the one I want to use.
I can type the passphrase for the key I want to use, and PGP recognizes it and prompts me, asking if I want to use that key for signing instead, and of course I answer "Yes". But why is PGP not providing the key in the drop-down list to begin with?
The key I want to use is active, not expired (no expiration date), enabled, signed, and has implicit trust.