I am sorry Bob, but qualiifying the ComboBox didn't help:
I modified the code to
Dim i As Intege
r = Range("AR5000").End(xlUp).Ro
For i = 2 To
Worksheets("QUERY_BUILDER").ComboBox3.AddItem CStr(Sheet1.Range("AR" + CStr(i)).Value
Nex

But I am getting the same error.