IT appears to be an issue with the function: InstrB always returning 1 even when that isn't the correct value.
A search of the web found others with the same problem: http://stackoverflow.com/questions/34181411/uploading-a-file-in-classic-asp
It has been a decade since I've worked with classic ASP, so I'm afraid I can't do much with it. Hopefully the user comments on that forum will help you.