Can't decrypt test message

[davkt]

Hi All,
I'm new to this so am willing to bet I'm making a daft mistake and not searching for the right thing to get a simple answer but here goes!
I think I've followed the instructions for installing Enigmail and openpgp, creating and publishing my key and have followed the instructions in the quick start guide for sending a signed message to Adele the robot. Adele sends me back an encrypted message but when I try to decrypt it I get an error message:

Error - secret key needed to decrypt message

gpg command line and output:
gpg
gpg: encrypted with 1024-bit ELG key, ID 62BDBFD4, created 2002-03-06
"Adele (The friendly OpenPGP email robot) <adele-en@gnupp.de>"
gpg: decryption failed: No secret key

I'm using Enigmail version 1.4.2 (20120519-0100) on a Mac running Lion and Thuderbird 12.0.1
What am I doing wrong?
Thanks
David