OK, I solved the problem by using a posted message to perform the
calculation. That way, the OnCalculateField event can complete it's
processing before the message is caught and used by the form. It seems to
have solved the problem so I will stick with it.

When I get a little more time, I'll try to look into exactly why the
calculation screws up the grid control, unless someone else already knows.

Thanks,

Woody (TMW)