Can't get combo box in user form to populate

Hi all,

I'm building a user form to input data to a sheet. Everything works except the combo box, which won't populate. I've tried the forums here, Microsoft help, and YouTube, but I can't find anything wrong with the methods I've tried. I'm pretty new at this, so it's probably some obvious difference between the instructions and my code that I'm not noticing. Here's my original code:

Option Explicit

Sub userform_intialize()
    'Fill combobox in the form
    With UnitTypeUserForm.UnitTypeCB
        .AddItem "Option 1"
        .AddItem "Option 2"
        .AddItem "Option 3"
        .AddItem "Option 4"
    End With
    'UnitTypeUserForm.UnitTypeCB.ListIndex = 0
End Sub

When this didn't work, I tried a different style:

Option Explicit

Sub userform_intialize()
    'Fill combobox in the form
    UnitTypeCB.List = Array("Single-family Home", "Apartment Floorplan", "Condominium", "Commercial Property")
    'UnitTypeUserForm.UnitTypeCB.ListIndex = 0
End Sub

I've placed this code in "ThisWorkbook" and the form code module and I've tried commenting out the list index line in case it was causing problems. No matter what I've tried, the combo box is always blank. Any suggestions?