application defined or object defined error

A few things that I notice

Range("CompSubBranch") = Empty

Empty is used as an unitialized vaiable. Just use

Range("CompSubBranch") = ""

For a validation (between) I expect a Formula like

Formula1:="1", Formula2:="3"

I would not use this : Sheet1.Protect

Instead

Dim Ws1 as Worksheet

Set Ws1 = Worksheets("Sheet1")
Ws1.Protect

why have

        .InputTitle = ""
        .ErrorTitle = ""
        .InputMessage = ""
        .ErrorMessage = ""
        .ShowInput = True
        .ShowError = True

When the strings are "" (empty) ?

I understand that your rng goes upto Q200, but where it could go wrong:

Function GetRange(val As Integer) As String
   Dim startPnt As Integer 
   Dim endPnt As Integer
   For Each Item In Range("'List'!Q2:Q200")
    If Item.Value = val And startPnt = Empty Then startPnt = Item.Row
    If Item.Value = (val + 1) And endPnt = Empty Or Item.Value = Empty And endPnt =Empty Then endPnt = Item.Row - 1
  Next
   GetRange = "$P" & startPnt & ":$P" & endPnt
End Function

Use startPnt = "" and
An integer can take values up to 32,767.

startPnt = Item.Row, so theoretically it can become as large as Cells.rows.Count, which is already 65,536 in XL2003.
This will give an overflow error '6'

Where it goes wrong (I think) is here Range("'List'!Q2:Q200")

   Set WsList = Worksheets("List")
   For Each Item In WsList.Range("Q2:Q200")