I have tried various methods:

1.Copy sheet from within workbook
2.Add new sheet and just copy the cells from master sheet
3.Add new sheet from template locaton rather than within workbook

and come to the conclusion that something in the spreadsheet itself may be
causing the problem.

I can add as many sheets as I like from VBA on any workbook except the one I
want to !

I have also discovered that when the error occurs any subsequent attempt to
run the macro fails and sheets cannot be copied, even when done manually. If
all the copied sheets are deleted to put the workbook back to its original
state and then it is saved the macro does not work at all when you re-open
the workbook. Neither can sheets be copied manually.

This suggests that Excel is storing some kind of marker wrt the number of
copied sheets which is not cleared simply by deleting them. I don't think it
is memory limit as I have successfully copied up to 200 sheets and consequent
file size of 3MB on another workbook.

If anyone knows how to clear this it would eliminate the problem.

In the mean time it looks like I might need to start from scratch to
recreate the worksheet I need to copy.