Check the minimal requirements regarding .NET packages. Also investigate which version clr.dll has and to which .NET package it belongs. All .NET packages are supossed to live with each other and should complent each other, also supporting multiple version of the same DLL.
When googling this you see many problems regarding .NET 4.0, you can either deinstall .NET4 and install .NET 4.5, or look at this solution:
You're best bet is to update all .NET version and install the .NET packages which you do not have.
We have .NET1, .NET2, .NET3, .NET3.5, .NET4, .NET4.5 & .NET4.51.
*note* Ooh and I'm not sure 'bout .NET1: I haven't encountered any application which needed this and I'm not sure if W7 supports it.