Well, I uncommented and changed one of the main lines and put another in place due to issues with https since our site runs on SSL:
url=(ssl?"https://":"http://")+String(Request.ServerVariables("HTTP_HOST"))+url;
url="https://"+String(Request.ServerVariables("HTTP_HOST"))+url;
Now I'm able to add a category whereas I couldn't before. However, whilst I'm able to upload images and get the message "x file(s) have been uploaded!", I get the immediate error "System error: -2146697191." in a dialog box. Refreshing the page gives:
"msxml3.dll error '800c0019'
System error: -2146697191."
/aspgallery/include_aspgallery.asp, line 58 which is "xh.send("");"
I've got the most recent versions of MSXML installed.