I have downloaded WUD v2.25 and tried running it on a Windows 2000 computer. But instead I hit an exception error when I try to add an update list (via clicking on the "+" button). At first I thought its because Win2k can't support it. But now I tried it on a Windows XP computer and clicking on that button brings me to WUD's website. What is wrong with this software? I have already installed all the necessary .NET software and updated them to no avail.

After installing WUD, you must download the appropriate Update List from the website.

I already have the Update Lists right next to the installer. The problem is I can't add them to the program.

Are they in UL or ULZ format?

Oops, I found the cause. There wasn't anything on your website about double clicking the list itself
There was only a vague mention there about opening instead of saving the Update Lists. This I didn't realize as I would normally download it first for archiving. Would be helpful to mention that on your website as well as provide a link there to this support forum.