Getting Name Error With Module

I defined function ConcatenateIf() in Module 1, that would take a range and combine the cell contents:


Function ConcatenateIf(iRange As Range, iLook As String, iNum As Integer)
For Each cell In iRange
If cell.Value iLook Then
ConcatenateIf = ConcatenateIf & Chr$(10) & cell.Offset(0, iNum).Value
End If
Next cell
End Function

Works beautifully. Then I save, and close. When I re-open, all the cells that reference this function display #NAME? error, like it can't find the ConcatenateIf() function. Does this have something to do with macro security? If so, why would it work at first, and then stop working?