I bought Oblivion the 5th Edition when I saw it in my local game store and I also have Oblivion GOTY Edition (retail), so I thought why not install the 5th Edition just to see if there were any differences between these versions and yes it was a difference.

I'm using Mircosoft.NET Framework 4.0 and that's working without any problems with both Morrowind GOTY & Oblivion GOTY (both retail), but it won't work with Oblivion 5th Edition when I launch Oblivion from the desktop shortcut and that has something to do with the JIT (Just In Time) module in .NET. Is there a patch that I need to install or is it something else I need to do here?

Thanks in advance.

GOTY Edition and the 5th Anniversary Edition are identical except for the packaging. They shouldn't behave any differently from eachother, however if you're trying to install both at the same time then you can encounter problems.

They're different because the 5th Anniversary Edition install DirectX9.0c and was already patched to the 1.2.0416 version with disc one, which the GOTY Edition didn't install DirectX9.0c and you need to install disc two before it was the 1.2.0416 version.

I don't know how but it seems the problem has been solved with a re-installation.