Ok, does it always work when you debug locally? If so, check whether both
systems have the same exact System.Transactions. In particular, make sure
the version, culture, and PublicKeyToken are exactly the same on both
systems.

Also, things don't usually change for no reason. Try to characterize the
times it stops working. For instance, does it stop working at a particular
time of day? Is there anything interesting in either the Application or
System event logs on either the local or remote systems when it stops
working?

I'm not as deep on this area of the CLR as I'd like to be, so these are
general troubleshooting tips. If these don't get you anywhere, you should
consider posting this question in the microsoft.public.dotnet.framework.clr
or microsoft.public.vsnet.debugging newsgroups (not both at the same time,
please).