I think I may be on to what may be the cause of this error, but I'm not sure.
I think that I'm hitting the issue where UDFs are not allowed to modify other
cells in the WS. It appears that when I actually have a UDF called from a
cell, it sets up the condition that my other function that is invoked by the
Worksheet_change event is no longer allowed to alter cells. I'm not sure what
cells it would be allowed/not allowed to change.

it might be some how related to the order the functions are called when the
WS recalculates or some other condition.

I changed the WS_change called routine so it sets public global vars and had
one set of cells that I changing get the global values and the error didn't
happen.

From my debug.print statements, I don't see why the WS_change invoked
routine should get caught up in the UDF limitation, or why the WS_change
routine is allowed to alter cells when there is no UDF on the WS.

Any ideas for a workaround? Any ideas how to allow my WS_change routine to
alter cells?

Thanks.