OpenNetCf dlls

For my smartdevice application, I use the OpenNETCF.Windows.Forms.dll. So i
added the DLL to the OS. But when I run the application, I get an exception
"MissingMethodException": File or Assembly name "OpenNETCF.Windows.Forms" or
one of its dependencies was not found.

Then I put all the OpenNetCF dlls in my OS, but I still get the same

I don't get my mistake. Any idea?