Function to get Usedrange gets error 91 - excel

Question

Trying to write a Union of Ranges Function
I get `Object variable or with block not set"
I am not getting this right (I think):
With Rng
UnionRange = Intersect(ws.UsedRange, Rng.EntireColumn)
End With
Sub iUnionRange()
Dim R As Range
'Check to see if the Function is working
Set R = UnionRange("Elements", Range("A1:D1, G1:G1, I1:K1"))
R.Select
End Sub
The Function
Function UnionRange(shtName As String, Rng As Range) As Range
Set ws = ThisWorkbook.Sheets(shtName)
If Rng Is Nothing Then Exit Function
With ws.Rng
UnionRange = Intersect(ws.UsedRange, .EntireColumn)
End With
End Function

Answer 1

First of all, use Set keyword to assign an object to a variable, so UnionRange = should be Set UnionRange =. Specify a sheet object when you are retrieving a range, doing so it's not necessary to pass sheet name to the function since Rng.Parent returns the sheet object.
There is example below:
Sub test()
Dim Q As Range
Dim R As Range
Set Q = Sheets("Elements").Range("A1:D1, G1:G1, I1:K1")
Q.Select
Set R = UnionRange(Q)
R.Select
End Sub
Function UnionRange(Rng As Range) As Range
If Rng Is Nothing Then Exit Function
Set UnionRange = Intersect(Rng.Parent.UsedRange, Rng.EntireColumn)
End Function

Answer 2

Your function is returning an object so you need to use 'Set', ie:
Set UnionRange = Intersect(ws.UsedRange, .EntireColumn)
I think your code might also also throw an error if 'R.Select' is called when the "Elements" worksheet isn't active (ie the user has activated another sheet). I wonder too if you're using the Range parameter as simply an address of cells when it can do a lot more for you.
If it were me, I'd change the code to the following:
Sub iUnionRange()
Dim ws As Worksheet
Dim r As Range
' Define the worksheet
Set ws = ThisWorkbook.Worksheets("Elements")
' Call the cell selection function
Set r = UnionRange(ws.Range("A1:D1, G1:G1, I1:K1"))
' Note, if you go to the properties of the "Elements"
' worksheet, you can change its name property to,
' say, ElementsSht and simply refer to the object by that name.
' As well as being easier to code, it does protect you
' from an error if a user changes the sheet name in
' Excel.
' So you could just uncomment the following line:
'Set r = UnionRange(ElementSht.Range("A1:D1, G1:G1, I1:K1"))
' Select the target range
SafeSelect r
End Sub
Function UnionRange(target As Range) As Range
If target Is Nothing Then Exit Function
Set UnionRange = Intersect(target.Worksheet.UsedRange, target.EntireColumn)
End Function
Sub SafeSelect(target As Range)
' Check that the range object is not nothing
' and the worksheet to be selected is active
If Not target Is Nothing Then
target.Worksheet.Activate
target.Select
End If
End Sub
If you're intending to call this routine a lot then perhaps define the UsedRange outside the scope of the function as you only need to process that command once to have the range defined. And finally, be aware that you could have some empty cells selected, especially at the bottom of your used range if some columns are shorter than others.
Good luck with your project.