FormattingGanttBar in a Master Project

[RNobleman]

I've written a macro to format the Gantt bar based on a custom
resource field that contains various colors. The macro works fine on
individual projects, but not in a master project. When I run it, I get
the following error: "Argument not valid" on the FormatGanttBar line.
There are only two arguments on that line: TaskID and MiddleColor.
Here is my code. Any suggestions of how to make it work for a Master
Project would be much appreciated. Thanks.

Sub Format_Gantt_Bar_by_Resource()

Dim myTask As Task
Dim ResourceID As Long
Dim ColorToApply As String

For Each myTask In ActiveProject.Tasks
If Not myTask Is Nothing Then 'check Task Is Not blank /
’missing’
If Not myTask.ExternalTask Then
If Not myTask.Summary And Not myTask.ResourceNames = ""
Then ' Not a summary task or blank resource field

ResourceID = myTask.Resources(1)

ID = FieldNameToFieldConstant("Gantt Color", pjResource)
ColorToApply =
ActiveProject.Resources(ResourceID).GetField(ID)

If ColorToApply = "Red" Then
ColorNumber = pjRed
ElseIf ColorToApply = "Black" Then
ColorNumber = pjBlack
ElseIf ColorToApply = "Blue" Then
ColorNumber = pjBlue
ElseIf ColorToApply = "Fuchsia" Then
ColorNumber = pjFuchsia
ElseIf ColorToApply = "Gray" Then
ColorNumber = pjGray
ElseIf ColorToApply = "Green" Then
ColorNumber = pjGreen
ElseIf ColorToApply = "Lime" Then
ColorNumber = pjLime
ElseIf ColorToApply = "Maroon" Then
ColorNumber = pjMaroon
ElseIf ColorToApply = "Navy" Then
ColorNumber = pjNavy
ElseIf ColorToApply = "Olive" Then
ColorNumber = pjOlive
ElseIf ColorToApply = "Purple" Then
ColorNumber = pjPurple
ElseIf ColorToApply = "Silver" Then
ColorNumber = pjSilver
ElseIf ColorToApply = "Teal" Then
ColorNumber = pjTeal
ElseIf ColorToApply = "White" Then
ColorNumber = pjWhite
ElseIf ColorToApply = "Yellow" Then
ColorNumber = pjYellow
Else
ColorNumber = -1
End If

If ColorNumber <> -1 Then
'Apply color to the Gantt Chart
GanttBarFormat TaskID:=myTask.ID,
MiddleColor:=ColorNumber
'Success

End If


End If 'myTask Is Summary
End If 'myTask Is Nothing
End If 'myTask.ExternalTask
Next

End Sub