That sounds a little odd. I need a little more info to help you. However, this post belongs in the Help: MOD Implementation forum, and not in the MOD Add-On Forum (W/Code).
Which version of the forum are you using? Have you done any changes to the file? Did the error happen recently or have you just added the mod? Could you post a link to a text-version of inc_activeusers.asp, so that I can take a look at the code?