I'm having a very strange problem.   We've got a handful of windows services
that communicate with a common service using remoting, in a publish/subscribe
type arrangement: services "register" for notifications, passing an interface
on which to callback.

ALL of the services are able to receive callbacks from the publising service
just fine - except one.  In this one case, when the async callback gets
called, we receive the following exception when we attempt to call EndInoke
to complete the call:

"Because of security restrictions, the type {our type} cannot be accessed"

This is the only information we get - no other clues as to what might be
wroing.  And like I said - at the very same time, all the other services
receive callbacks just fine.  Really wierd.

If anyone can even point me in a direction as to how I can trouble shoot
this, it would be much appreciated.   I'm pulling what's left of my hair out.

Thanks!