RSA cryptography

I'm trying to encrypt xml documents using rsa encryption and I decided to follow the example on msdn's website at this link: http://msdn2.microsoft.com/en-gb/library/ms229746.aspx 

I combined that code together with the decryption example (which is linked to on that page and also here: http://msdn2.microsoft.com/en-gb/library/ms229919.aspx) but the resulting program does not work - I get an exception saying that it cannot find a decryption key. Its very possible that I simply don't understand how C#'s rsa api works. Any help would be appreciated.