Keeping tech support on the latest software version

Question

I'm the only software developer maintaining a subset of products at a small company. The main product I'm concerned with here is a web app which is installed on various clients' machines, with a database and background processes.

I make changes on a need-to basis for this program. It's not the company's flagship product, it's not my main project, but it needs maintenance. I have 2 and a half support technicians who take in questions from customers. When they don't know how to fix things, I'm their support.

Because I do some maintenance here and there, I release updates irregularly. However, the idea is that I'm fixing the software, and on a client's request, the support technicians can update said software to fix an issue or as good measure (there's no built-in update function). The support technicians also keep a copy on their machine, or rather, various copies of past versions. This is where it gets ugly.

I get, irregularly, reports of bugs for things I might have already fixed on previous versions. When they find a bug, the support techs spend a lot of time going backwards in versions, trying to get to a version where the bug isn't there. At this point they either throw it in my face ("Why did you break this?") or install older versions at the clients'. Which can obviously break other things.

In order to resolve this I've:

• pleaded with them
• pleaded with their supervisor
• pleaded with the CEO
• refused to work on older versions until new versions are installed, even if they demonstrate the bug is still present
• threatened to remove support altogether (which is moot, since it's still my job)

No dice.

The last option I see is to setup something with SVN where they can only get the latest version and not revert (if that's doable)... And hope they don't learn to make copies.

Is there some other approach, human, organizational, technical, or otherwise that can help me and keep these guys on the latest version?