Ive run in to trouble with my .Config file exposing types that were written with typos and such. The remoting framework will not tell you it could not load the file, unless you explicitly tell it to:

just before closing the "system.runtime.remoting" xml node, add this node:

</application>

<debug loadTypes="true"/>

</system.runtime.remoting>

now you'll get an exception the next time the remoting service could not expose your type for whatever reason...