I do not see the cause of the problem.

For these entries;
line A B C
23 4006 200 4206
24 100 50 4256 All are formatted numbers
A&B get keyed in C is =C23+A24-B24
25 10 4266 All are formatted numbers
A&B get keyed in C is =C24+A25-B25

This formula in C gets dragged down from line 2 with no problem for about
30 lines then starts returning #VALUE "a data point in the formula is of the
wrong data type".
I checked and columns a-b-c are formatted as numbers I tried as general
then back to numbers. No luck.
What is MY error please and how do I fix it. This file was in 2003 or maybe
even one version earlier as xlm but I saved it as xlsm in Excel 2009, its
now showing (compatibility mode)
Mel