I have a ClickOnce app in production and a support case was opened where the ClickOnce installer was producing the following error:
"This operation is only supported on Windows 2000 SP3 or later operating systems."
The weird thing is that the computer this error was happening on was Windows XP Professional SP2. So what gives? After a lot of heartache and tears :-p the solution eventually presented itself. The app was attempting to run in compatibility mode. In the case of my ClickOnce application, I had a WinForms app that was a launcher. It would spawn an IE process and navigate to the ClickOnce install URL. On this particular machine this WinForms app was set to run in Windows 2000 compatibility mode so it was launching the IE process in the same compatibility mode.
I have no idea how the compatibility mode was set on the WinForms app. The user of this computer does not seem capable of knowing how to set this. However, once unchecking the compatibility mode all was well again. This would likely effect any .NET application, not just a ClickOnce application. But it caused me enough grief that I had to post the solution.