64 bit SolidWorks and Add-in problem

I have developed a C# addin project for SolidWorks 2010.  When I install the addin in 32-bit machine it is working normally.

But When I install it to 64-bit machine, it installs normally, but I start SolidWorks 2010 64 bit, the addin is not visible.

So What can be problem ?  Thank you

SolidworksApi macros