Is there any reason that it would'nt work on version 2.0.20?
Not that I'm aware of.
I really don't want to upgrade and loose my mods already installed or go throught reinstalling.
I can understand your predicament. On the other hand, you have to realise that keeping your phpBB board up-to-date is crucial for security reasons. With a proper database backup (including any and all tables created by MODs) and a forum backup, there is no justifiable reasons to remain out of date as you are. Are you familiar with the "Code Changes" package to help you retain your installed MODs while updating to the most recent phpBB version?
My web site developer tried to install the User Shield mod today, didn't get any errors (that he mentioned) but can't seem to see it anywhere (ACP or memberslist drop down). Any help or suggestions would be fantastic.
Was the installation done manually? Was the required database update done? If you take a look at the 3rd post on the 1st page, there are screencaptures as to what you should visually expect when User Shield is installed, logged in as an admin. and as a user. What's missing versus your installation?
Let me know about the above and we'll take it from there.