Are you sure, the LED works?
You can use a battery with a resistor in series to test it in the circuit,
but if you can, you should disconnect it from the Dout first.
Did you add
DOUT_ENTRY TMP5, 5, x, y ; LFO Positive LED
below "CS_MENU_DOUT_TABLE" in setup*.asm?
( with x=number of shiftregister and y=pin, e.g. 6,3)