passing variables to subroutine from userform

Hi, I'm relatively new to VBA excel programming and have gotten stuck on this problem. I have a sub procedure that is intended to load a list of values into a combobox; I wish to call this from a userform. The call from the user form needs to nominate/pass these variables so the called subroutine can identify the range for the values. The called subroutine is located in a separate module called "mod_ListboxTools".
Although I've spent some time looking (and experimenting) for what may be at issue my lack of VBA programming concepts is most probably bring me unstuck.
Any assistance appreciated.

Calling sub() located in a Userform

'***********************************************************************
'*  Load a unique list of entries into a form's list/combo box list.
'*
'*  inputs
'*      cboName = "cbo_pdtWghtForm"
'*      shtName = worksheet holding input range i.e. "Table 3.3A"
'*      rngName = input range for combo box     i.e. "Wrought Form"
'*
'***********************************************************************
Private Sub cbo_pdtWghtForm_Enter()
Dim shtName As String
Dim rngName As String
Dim cboName As Object
Dim ufrmName As Object

Set ufrmName = ufrm_1MechProp
Set cboName = cbo_pdtWghtForm

shtName = "Entry_Arrays"
rngName = "PdtForm_List"

'call subroutine to load vaiables
mod_ListboxTools.ComboLoadList shtName, rngName, cboName, ufrmName

End Sub

Called subroutine that is located in a module called "mod_ListboxTools"

'***********************************************************************
'*  Subroutine called from a userform to load a unique list
'*  of entries from a worksheet range into a combobox list.
'*  Uses a loop to step through each cell in a Worksheet.Range
'*  and adds each range value to a list/combo box list.
'*  If a range value is blank, it is not added.
'*
'*  inputs
'*      frmName = form name
'*      cboName = combobox to load list with    i.e. "cbo_pdtWghtForm"
'*      shtName = worksheet holding input range i.e. "Table 3.3A"
'*      rngName = input range for combo box     i.e. "Wrought Form"
'*
'***********************************************************************
Sub ComboLoadList(shtName As String, rngName As String, cboName As Object, frmName As form)

Dim Cell As Range

' clear the contents of the combo/listbox
' set combo/listbox prompt value
' load values from range into combobox "cbo_pdtWghtForm"
' select only non-empty values

With frmName
cboName.Clear
cboName.Value = "Select Product Form"
    For Each Cell In Worksheets(shtName).Range(rngName)
        If IsEmpty(Cell) = False Then
            Cell = Trim(Cell)
            cboName.AddItem Cell.Value
        Else:
        End If
    Next Cell
End With
End Sub

Hi Norie,
Thanks for getting back, When stepping through the calling routine it hits the call statement at this line in the code and comes up with an error 13 - as below.

'call subroutine to load variables
mod_ListboxTools.ComboLoadList shtName, rngName, cboName, ufrmName

7-06-2013 3-20-11 PM.jpg

I've altered the called routine first line but still have the problem as described.

Sub ComboLoadList(shtName As String, rngName As String, cboName As Object, frmName As Object)

Dim Cell As Range

Hi Norie,
Mea Culpa!
(crap! - spent a long time trouble shooting a problem that was the code but not the code)

I had the same called routine in the userform code area - effectively repeating the code in two places. During trouble shooting I copied this into the same area to compare the code/s. It all runs now and looks like the following. Thanks for your assistance.

Option Explicit
 Option Base 1
'***********************************************************************
'*  Load a unique list of entries into a form's list/combo box list.
'*
'*  inputs
'*      cboName = "cbo_pdtWghtForm"
'*      shtName = worksheet holding input range i.e. "Table 3.3A"
'*      rngName = input range for combo box     i.e. "Wrought Form"
'*
'***********************************************************************
Private Sub cbo_pdtWghtForm_Enter()
Dim shtName As String
Dim rngName As String
Dim cboName As ComboBox
Dim ufrmName As UserForm

Set ufrmName = ufrm_1MechProp
Set cboName = cbo_pdtWghtForm

shtName = "Entry_Arrays"
rngName = "PdtForm_List"

'call subroutine to load vaiables
mod_ListboxTools.ComboLoadList shtName, rngName, cboName, ufrmName

End Sub

called sub() as below

'***********************************************************************
'*  Subroutine called from a form to generate a unique list
'*  of entries from a column of data into a combobox list.
'*  Uses a loop to step through each cell in a Worksheet.Range
'*  and adds each range value to a list/combo box list.
'*  If a range value is blank, it is not added.
'*
'*  inputs
'*      frmName = form name
'*      cboName = combobox to load list with    i.e. "cbo_pdtWghtForm"
'*      shtName = worksheet holding input range i.e. "Table 3.3A"
'*      rngName = input range for combo box     i.e. "Wrought Form"
'*
'***********************************************************************
Sub ComboLoadList(shtName As String, rngName As String, cboName As ComboBox, frmname As UserForm)

Dim Cell As Range

' clear the contents of the combo/listbox
' set combo/listbox prompt value
' load values from range into combobox "cbo_pdtWghtForm"
' select only non-empty values

'With frmname
cboName.Clear
cboName.Value = "Select Product Form"
    For Each Cell In Worksheets(shtName).Range(rngName)
        If IsEmpty(Cell) = False Then
            Cell = Trim(Cell)
            cboName.AddItem Cell.Value
        Else:
        End If
    Next Cell
'End With
End Sub