Another EMC Q: won't get out of Estop!

I recently upgraded from EMC 2.0 to 2.16 after
having the older version more or less working.
But now it refuses to come out of estop. I've
tried dfferent combinations of limit switch polarities
with no luck. I have debugging messages fully on but
nothing unusual is being reported. Does anyone know
of any other possible causes of the task state
getting locked in estopon ? I've tried grepping thru
the source a bit, but the code is far too modular.
Gratefull for any hints,

Robert