Definitely a bug of some kind. Can you visit our support form and send in the workspace and the full log and we'll take a look. Sorry about this one.
This mostly happens when u reference a parameter wich at that point has not been created yet.
I encountered this error before, and it always was due to malstructered script.
If i'm not mistaken, you can get this using variable setters and readers.
I suggest checking the structure of your script.
@kborgwardt,
I encountered the issue this afternoon as I was tinkering with python code written by someone else. It turned out that in the commented-out sections, there were references to the offending variables in the form of $(my_var). I guess even though the references are commented out in python code, FME interpreter still treats $(my_var) as a special variable or parameter.
I removed the "$(" and the workspace worked now.
Hope this helps.
Bo