I have 2 sets of keys on my Windows 7 system with GPG4Win tools installed (including Kleopatra key management) and 2 Enigmail-based email clients (Thunderbird + Seamonkey) and Claws, which uses an own plugin.
One key pair works as expected. Shows up in Kleopatra and in the Enigmail/Claws key management (sometimes twice there). It can be used for signing and decryption.
The other one acts up. It shows ok in Kleopatra, but with an empty line after "Certificate Usage:" (The other key shows "Signing EMails and Files, Encrypting EMails and Files, Certifying other Certificates" here.) It does not show up in the Enigmail/Claws key management and is reported missing during encryption in Enigmail and as a "Unsupported Protocol" in Claws.
If I export the (private) key from Kleopatra and import in Enigmail/Claws, I'll get just nothing from Enigmail (No error message, no update to the list of keys) and a confirmation of importing 1 private and 1 public key from Claws, but still no update to the list.
The exported key file has some content, but I can't really tell if its ok or not.
The key in question was successfully used to sign and decrypt mails before on that machine, although some time ago.
How do I analyze the key further? What properties of the key does the missing line in Kleopatra correspond to? Can a key 'loose' its ability to sign/decrypt? How can the key be repaired?