I know its a very old post, still i think it should have some hints to the solution.
The error says it is not able to calculate the domain of values for the field 'STATE'
As you said, values are all 2 character abbreviation. However, i'm guessing in the same stream you are getting another value called 'STATE'. Kindly add a filter to this connection to remove 'STATE' from the result. That should solve the problem.