IIS is preventing my ASP driven CAPTCHA from working outside the LAN. It worked fine for five years until I had to run SBS 2003 CEICW the other night to renew the Self-certificate. I don't remember what I did five years ago to make this work. CEICW obviously changed some security setting since the CAPTCHA ASP executes on the a LAN but not on the WAN.
The CAPTCHA ASP I am using can be found on www.webwiz.co.uk