Dave,
I did encounter one oddball issue that no one else seemed to be able to duplicate.
I had a Rev.L TIU connected to a WIU via USB and also had a plain old 9-pin, straight-through, 6' cable connected to the Rev. L's serial port, with nothing connected to the cable's other end. Until I removed the serial cable, the app had major heartburn using that TIU.
Does this sound at all familiar?