.Net 3.5.1 is installed as part of Windows 7 so 2.0 will not install and informs you to use the "Turn Windows Features on or Off" section in Control Panel. So I disabled 3.51 and then re-enabled. I also ran a repair on 4.5.1 framework which is also installed but as a program.

No change I'm afraid. But thanks for the suggestion it sounded very plausible. Something must be corrupt somewhere.

I could try removing 4.5.1 I suppose...

MS200, UHD722, DSP5200(SL), Roon