Can't generate ProjectServerServices.dll Proxy using Project Server SDK.

I am trying to use PSI for project server 2010 programming. For that I have to generate proxy of project server WCF or web service.

So I used 'GenWCFProxyAssembly' command & got below error.

 "error CS1548: cryptographic failure while signing assembly."

And "sn" is not recognized as a internal or external command.

thanks