Distributed Transaction problem

Hi,

I'm having problems getting transactions to work correctly in a state machine workflow. Within the TransactionScope activity I have a Code activity that does a couple of database writes, another Code activity that sends out a notification email, and a SetState activity, which I want to be executed only if the rest of the code executes correctly. The WF runtime and DB are hosted on different servers.

After fixing a "The partner transaction manager has disabled its support for remote/network transactions" error by enabling the MSDTC stuff on both machines, I'm now getting a new error:

"The transaction has already been implicitly or explicitly committed or aborted (Exception from HRESULT: 0x8004D00E)"

Although I've found seveal references to this error on this and other forums, I haven't actually found an explanation for why it happens, or how to get around it.

Any ideas or suggestions very gratefully received!

Cheers,

Dave