I dug around and found a site I maintain that still uses this reCaptcha. Although we have the forum registration disabled and redirecting to a single registration point using Solspace’s registratin module, I re-enabled the forum registration page temporarily, and it does work successfully.. still 😊
I’ve sent you a PM with a download link to a modified reCaptcha that I am using. It is not the latest version of the script, but I know it works in EE 1.7.1 with the latest forums module for EE 1.7.1.
I compared my register forum template with a virgin sample and they appear identical. Hopefully this will work for you. I’ve a nagging feeling that I had to do something slightly different to get the registrations to work in the forums. Sadly, I didn’t document it.