Tired of getting an error similar to "The object with ID implements the IObjectReference interface...", then try having different environments for testing workflows and another for developing them. This error is prevalent when you persist data through a workflow and then make some minor changes to it (Let's say when making a fix to a bug:) then publishing out a new workflow. The persisted data then becomes stale.
It is important, for all IT development to have different environments, that way the data is separated. Once changes are made to an actual workflow in your development environment which persists data, that data should be removed, so the whole workflow can be tested again.
I was able to find a post within the forums which also may be helpful.