That should not happen as the exception states. Can you post a bug report with a small reproduceable test case at source forge?
I've posted the above into a bug report:
I know that it's probably useless until I submit a bug report. It may take me awhile to get around to it (deadline to meet).
There is sort of a workaround in the meantime - use OBJECT() to retrieve the entity and get the field value that way.
Sorry, and thankyou for the response!!!