I've seen a thousand of these threads but none can solve my problem.

I have spreadsheets that I am referencing in my master spreadsheet, so cells contain formulas like: =C:/Documents/.... you get the idea. So my problem is, the blank cells on the supporting spreadsheets are appearing as 0 on the master spreadsheet. However, I am trying to make charts, and I want there to be no point for anything with a blank value, but instead I'm getting graphs with zero values instead of not showing up. I feel like there must be a vba code to solve this problem. I tried:
Sub noZero()
Dim rng As Range
For Each rng In Range("A1:N220")
If rng.Value = 0 Then
rng.Value = ""
End If
Next
End Sub
But I'm getting an error message on rng.Value = 0 so, not sure what is wrong with it. I'm using excel 2010. I can't just hide the 0 values, I need them to be deleted/replaced completely.

Thanks for your help!