>>>>>>Sounds right.
>>>>>>
>>>>>>Maybe you could try uninstalling NET Framework 4.0 and install again?
>>>>>>
>>>>>>Just a shot in the dark...
>>>>>
>>>>>If I remove it, how do I re-install it?
>>>>
>>>>http://msdn.microsoft.com/en-us/netframework/aa569263
>>>
>>>Thanks. For now I repaired installation and checking if it helps. I'm a bit afraid to uninstall .NET 4.0 - what if someone breaks?
>>
>>I've had to uninstall NET Framework versions in the past, and have not had problems (suprisingly).
>>
>>YMMY.
>
>Ok, I'll try it, as it again gives me this.
>
>So, which one I have to uninstall in Control Panel?

I'd go after anything that starts with Microsoft .NET Framework 4. On my machine I see Microsoft .NET Framework 4 Client Profile, Microsoft .NET Framework 4 Extended, and Microsoft .NET Framework 4 Multi-Targeting Pack.

It's possible you may need to uninstall some updates as well (you'll know because uninstall will fail on one or more of the main programs). Click on View Installed Updates in the menu bar on the left of Control Panel and you will see updates grouped by program. Mine has 11 updates listed for Microsoft .NET Framework 4 programs.