You're using the old NAI version of Command Line; it is not sold or supported by Symantec/PGP. I don't know that you'll get much help on it here; at the old PGP support forums nobody was familiar with that old version.
The only thing I can suggest (besides buying a copy of PGP Command Line 10 :-) ) is to try signing the key with a private key of your own. Note that PGP Command Line as sold by Symantec has been designed to work in a scripted environment and will never prompt you for input.