Thanks Tom.

Firstly, yes you are right, because this runs OK for the 1st few times
it it NOT a protection Issue.

We are using Excel 2,000.

We have tried setting the Buttons attribute "TakeFocusOnClick" = False
AND ActiveCell.Activate was the 1st Line (Even with a "DoEvents()"
thrown in on line 2, for good measure), all to no avail.

The Routine in question does have an "On Error Goto FunctionA_Err"
Handling Routine, with a Resume FunctionA_Out statement. But even
with a breakpoint Set ON, BEFORE the Resume statement, The VBA IDE
Degugger does not stop on any line in the Error Handling Routine. It
seems like Excel has not handed me back control before it bomed. (The
following comment is not intended to offend anyone, but it has nothing
to do with me making a mistake debugging (as I have being doing VBA
for yonks)).

Hope someone can shed some light on why multiple calls to change a
cell's ColorIndex should fail after 2/3 attempts, whilst using EXACTLY
the SAME VBA Function.

Thanks Again.