Chen-Chieh Feng wrote:

Program error: {instDirectPositions_v1683_v1697 dir_pt}

Could anybody give me a direction on how to read this error message and the possible cause of this error? Thank you very much.

Check wheter all pattern matches are complete, i.e. all constructors are matched. If you forget one, hugs says things like this. Another possibility is that you used records. Can you please tell a bit more about the program (source code)?