Error 9: Subscript out of range - vba

Question

I have a problem in excel Vba when I try to run this code, I have an error of subscript out of range:
Private Sub UserForm_Initialize()
n_users = Worksheets(Aux).Range("C1").Value
Debug.Print Worksheets(Aux).Range("B1:B" & n_users).Value
ListBox1.RowSource = Worksheets(Aux).Range("B1:B" & n_users).Value
ComboBox1.RowSource = Worksheets(Aux).Range("B1:B" & n_users).Value
ComboBox2.RowSource = Worksheets(Aux).Range("B1:B" & n_users).Value
End Sub
And Debug.Print works well, so the only problem is in Range("B1:B" & n_users).Value.

Answer 1

If the name of your sheet is "Aux", change each Worksheets(Aux) reference to Worksheets("Aux"). Unless you make Aux a string variable, for example:
Dim Aux As String
Aux = "YourWorksheetName"
n_users = Worksheets(Aux).Range(C1).Value
you must use quatations around sheet references.

Answer 2

Firstly, unless you have Aux defined somewhere in the actual code, this will not work. The sheet-name reference must be a string value, not an empty variable (which ARich explains in his answer).
Second, the way in which you are trying to populate the rowsource value is incorrect. The rowsource property of a combobox is set using a string value that references the target range. By this I mean the same string value you would use in an excel formula to reference a cell in another sheet. For instance, if your worksheet is named "Aux" then this would be your code:
ComboBox1.RowSource = "Aux!B1:B" & n_users
I think you can also use named ranges. This link explains it a little.

Answer 3

I can't see how you can get an Error 9 on that line. As others have pointed out repeatedly, the place you'll get it is if the variable Aux doesn't have a string value representing the name of a worksheet. That aside, I'm afraid that there is a LOT wrong with that code. See the comments in the below revision of it, which as near as I can figure is what you're trying to get to:
Private Sub UserForm_Initialize()
'See below re this.
aux = "Sheet2"
'You should always use error handling.
On Error GoTo ErrorHandler
'As others have pointed out, THIS is where you'll get a
'subscript out of range if you don't have "aux" defined previously.
'I'm also not a fan of NOT using Option Explicit, which
'would force you to declare exactly what n_users is.
'(And if you DO have it declared elsewhere, I'm not a fan of using
'public variables when module level ones will do, or module
'level ones when local will do.)
n_users = Worksheets(aux).Range("C1").Value
'Now, I would assume that C1 contains a value giving the number of
'rows in the range in column B. However this:
'*****Debug.Print Worksheets(aux).Range("B1:B" & n_users).Value
'will only work for the unique case where that value is 1.
'Why? Because CELLS have values. Multi-cell ranges, as a whole,
'do not have single values. So let's get rid of that.
'Have you consulted the online Help (woeful though
'it is in current versions) about what the RowSource property
'actually accepts? It is a STRING, which should be the address
'of the relevant range. So again, unless
'Range("B1:B" & n_users) is a SINGLE CELL that contains such a string
'(in which case there's no point having n_users as a variable)
'this will fail as well when you get to it. Let's get rid of it.
'****ListBox1.RowSource = Worksheets(aux).Range("B1:B" & n_users).Value
'I presume that this is just playing around so we'll
'ignore these for the moment.
'ComboBox1.RowSource = Worksheets(aux).Range("B1:B" & n_users).Value
'ComboBox2.RowSource = Worksheets(aux).Range("B1:B" & n_users).Value
'This should get you what you want. I'm assigning to
'variables just for clarity; you can skip that if you want.
Dim l_UsersValue As Long
Dim s_Address As String
l_UsersValue = 0
s_Address = ""
'Try to get the n_users value and test for validity
On Error Resume Next
l_UsersValue = Worksheets(aux).Range("C1").Value
On Error GoTo ErrorHandler
l_UsersValue = CLng(l_UsersValue)
If l_UsersValue < 1 Or l_UsersValue > Worksheets(aux).Rows.Count Then
Err.Raise vbObjectError + 20000, , "User number range is outside acceptable boundaries. " _
& "It must be from 1 to the number of rows on the sheet."
End If
'Returns the cell address
s_Address = Worksheets(aux).Range("B1:B" & n_users).Address
'Add the sheet name to qualify the range address
s_Address = aux & "!" & s_Address
'And now that we have a string representing the address, we can assign it.
ListBox1.RowSource = s_Address
ExitPoint:
Exit Sub
ErrorHandler:
MsgBox "Error: " & Err.Description
Resume ExitPoint
End Sub