Kevin,
There is no master control for Control Tips.
One thing that can cause this symptom is if you have
surrounded your controls with a rectangle control and:
1) the rectangle was added to the form *after* the other
controls were added.
2) or the controls were "sent to back" "behind" the
rectangle.
3) or the rectangle was "sent to front" in front of the
other controls.
Even if all items are completely visible to you, items can
still be "in front of " or "behind" the rectangle in which
case Access cannot tell that your mouse pointer is
hovering over the specific control that falls within the
area defined by the rectangle.
If this is the case, then you can solve the problem by:
1) Select the rectangle.
2) Select "Send To Back" from the "Format" menu.
Once these steps have been performed, the controls should
be "on top" so that Access can tell that your mouse
pointer is hovering over the controls, not the area
defined by the rectangle.