What you want to look for is called "NDR" - DCOM and RPC use the NDR engine and make calls to registered servers on remote boxes. That's why you got an RPC error.

I don't ever try to code this stuff in VB, but you can look up the RPC api's and try to make a very simple dummy app that calls your stub and try to debug what is happening.

Search for "RPC" then for "NDR" on MSDN