I think you're working with known issue. I reported this
to Microsoft about two months ago. The situation is as
follows:
If you create a winforms app in 1.0 (and your server
objects were also done in 1.0) and you install 1.1 on the
server then your problems begin. The issue is that IIS (I
am assuming you are hosting your remote components in
IIS) automatically uses the latest version of the .NET
Framework so when it goes to serialize any messages, it
finds that the version on the client is not the same as
the version on the server and throws an exception. One
way to check and see if this is the issue, check your
output window and you should see two DIFFERENT versions
of one of the System.* libraries (I found this because
two versions of System.Data were loaded).

Microsoft is looking into this right now.

Hope this helps.

The solution is to just upgrade the winforms client to
1.1 as well and everything will work just fine.

Jeff Levinson

Author of "Building Client/Server Applications with
VB.NET: An Example Driven Approach"