[Zack Barresse]

They're text. Try converting them...

    wk.Worksheets(MAIN_SHEET).Range("B6").Value = CLng(wk.Worksheets(DATA_SHEET).Range("BA3").Value) + CLng(wk.Worksheets(DATA_SHEET).Range("BB3").Value)

Works for me.

[slurpee55]

In 2003 it puts a little triangle in the corner to indicate that it is a number formatted as text and you just have to highlight all those cells and then click on the alert box to the side and it will convert them. Otherwise, if you click on the cell and then put your cursor into the formula bar at the top it will convert it to a number. But that is pretty time-consuming. Zack probably has a better way than that.
What version are you using?

[sk0101]

I am using Excel2007.
I tried Zack's formula and it worked!!!
Appreciate all of your help.

[slurpee55]

The CLng function converts it to long? Cool....

[Zack Barresse]

It is still seen as text when the Value is passed into memory via VBA, yes. Sucks, but it happens. You could populate a preset variable with the data as well without worrying about it ...

Sub populate()
    Dim wk As Workbook, wsDATA As Worksheet, r1 As Long, r2 As Long
    Set wk = ThisWorkbook
    Set wsDATA = wk.Sheets(DATA_SHEET)
    Let r1 = wsDATA.Range("BA3").Value
    Let r2 = wsDATA.Range("BB3").Value
    wk.Worksheets(MAIN_SHEET).Range("B6").Value = r1 + r2
    wk.Worksheets(MAIN_SHEET).Range("B11").Value = wsDATA.Range("B3").Value + wsDATA.Range("B4").Value
End Sub