Thank you for your suggestion!
You are right but after i do it so I can't built the project because the error occurred from the other .dll file.
That is CANbus dll file, Looks like they prefer the Target CPU to be X64 or AnyCPU.
I have .Net2 and .Net4 for the CANbus dll file but when I use .Net2 in this project the system said can't mix .net differ version.
Do you have any idea to fix this?