Cannot open 'MSCOREE.lib' using Windows7.1SDK

I'm using VS2010. I tried to change the target .NET framework from v.40 to v2.0 and according to this site:

http://msdn.microsoft.com/en-us/library/vstudio/ff770576.aspx

I should be usign the Windows7.1SDK platform toolset, but when using it I get the following error:

LINK : fatal error LNK1104: cannot open file 'MSCOREE.lib'

I've also tried using the v100 platform toolset but it compiles with the 4.0 framework, in runtime I get this error using v100:

Additional information: Mixed mode assembly is built against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.

The program '[8464] clr_console.exe: Managed (v4.0.30319)' has exited with code 0 (0x0).

How should I downgrade to v2.0?

Thanks.