Runtime error using range with variable name in it - excel

Question

I am getting a runtime error 1004: Method 'Range' of object '_Global' failed when running my code. It should be splitting the data in the source column into a destination specified by the first blank column in the array. Because the source data is erratically formatted it needs to look for tabs or line breaks as the delimiter. I am using variable names for the source and blank columns as they are not at a fixed position in the array.
Dim CurrentCol As Integer
Dim FirstCol As Integer
Dim LastCol As Integer
Dim ColName As String
Dim BlankCol As Integer
Dim Source As Range
Dim SourceCol As String
Dim SourceAdd As String
Dim FirstColName As String
BlankCol = ActiveSheet.Cells(1, Columns.Count).End(xlToLeft).Column + 1
FirstCol = BlankCol + 1
Cells(1, FirstCol).Value = "FirstCol"
FirstColName = Cells(1, FirstCol).Value
Cells(1, BlankCol).Value = "Unique Classes"
Set Source = ActiveSheet.Rows(1).Find("International", LookIn:=xlValues)
SourceCol = Source.Column
SourceAdd = Source.Address
Range(SourceAdd).EntireColumn.TextToColumns _
Destination:=Range("PatBase[[#Headers], [" & FirstColName & "]]"), _
DataType:=xlDelimited, _
Tab:=True, Other:=True, OtherChar:="" & Chr(10) & "",_
FieldInfo:=Array(Array(1, 1), Array(2, 1), Array(3, 1), Array(4, 1), Array(5, _
1), Array(6, 1), Array(7, 1), Array(8, 1), Array(9, 1), Array(10, 1), Array(11, 1), _
Array(12, 1), Array(13, 1), Array(14, 1)), _
TrailingMinusNumbers:=True
Once the data is in the columns I then have more code which truncates it to 4 characters with the range in the same format, but this is working fine:
CurrentCol = FirstCol
For i = FirstCol To LastCol
Columns(CurrentCol).Select
ColName = Cells(1, CurrentCol).Value
If ColName = "" Then
Exit For
End If
Selection.TextToColumns Destination:=Range("PatBase[[#Headers], [" & ColName & "]]"), _
DataType:=xlFixedWidth, FieldInfo:=Array(Array(0, 1), Array(4, 9)), _
TrailingMinusNumbers:=True
CurrentCol = CurrentCol + 1
Next i
I suspect I am missing something obvious but I'm not a skilled macro writer so am at a loss. Can anyone help?