Just a couple of suggestions....

Many personal firewalls now have an integrated IDS. If this is the case with his your port scans may be failing because the scan is to agressive. Try slowing the scan down to the slowest speed. Maybe you can sneak something through.

You could also try spoofing the IP address to make it look like the requests comming from your computer are comming from his. Here again most personal firewalls and IDS will detect this but he has probably left you a hole somewhere.

Good luck.