32 bit System.Data.dll picked up in 64 bit exec

When compiling for 64 bit, I get an error saying that the assembly System.Data.dll targets different processor.

It's picking up System.Data.dll from C:\Windows\Microsoft.NET\Framework\v2.0... 

There is another System.Data.dll in C:\Windows\Microsoft.NET\Framework64

I'm not sure why is that not being picked up...

Also, in C:\Windows\Microsoft.NET\Framework and C:\Windows\Microsoft.NET\Framework64 there are sub directories for the different .NET versions, yet I pick up a System.Data 2.0 on a 3.5 project.

Some of my other 3.5 assemblies listed in the Reference Manager are located in C:\ProgramFiles(x86)\Reference Assemblies

Wouldn't the best if it was referencing the files from C:\Windows\Microsoft.NET\Framework ?