The following code works when the DATAX sheet is activated; but when another
sheet is selected/activated, it generates an error "1004
Application-defined or Object-defined error"

can someone tell me what I did wrong??

Worksheets("DATAX").Range(Cells(3, 9), Cells(beginrow - 1, 9)).Formula =
Worksheets("DATAX").Cells(3, 9).Formula