Bad news
A very similar thing happened to us. This guy is trying to make a living by ripping people off.
He originally contacted us for software and was interested in leasing. When he learned that the software needed date codes every few months to unlock, he immediately requested purchase pricing. He said it looked good and we sent over a purchase agreement for the system.
He couriered a cheque, next day service, and we thought the same thing as blackice, 'wow what a great guy'. The cheque appeared to clear in the bank, and a week later he was literally hounding me for the full unlock code. Eventually when all appeared well in the bank after a lengthy period of time, we provided the unlock.
21 full days after we had received the cheque originally, the bank returned it citing a stop payment. We attempted to reach Steve many times, and when he got sick of us calling he sent an email threatening to charge us for harassment.
We attempted to bring the police into the matter, which unfortunately did not go very far, and we ended up sending his account to collections, ensuring it would be a black mark on his credit report. Still have none of our money. This all happened back in March.
WATCH OUT FOR THIS GUY