Error 0 in Visual Basic 6.0

I have the following stored procedure in MS SQL server that I call in VB 6.0 to add data to the table.

CREATE proc sp_Add_Premises
     @Prem_Name varchar(50),
     @Prem_PhysicalAddress varchar(200),
     @Prem_Phonenumber varchar(50),
     @Town_id int
     
as
     if exists(select Prem_Name from Premises where Prem_Name = @Prem_Name)
     begin
          raiserror('The premises already exists.Specify another one.',16,1)
          return
     end
     if len(@Prem_PhysicalAddress)=0
     Begin
          raiserror('You must input the physical address of the premises before clicking on add.',16,1)
          return
     end
     --if len(@Prem_Phonenumber) = 0
     --begin
          --@Prem_Phonenumber='Missing Telephone'
     --end
     if @Town_id = 0
     Begin
          raiserror('You must specify the town in which it belongs first.',16,1)
          return
     end
     else
     begin
          insert into Premises(Prem_Name,Prem_PhysicalAddress,Prem_PhoneNumber,Town_ID) values(@Prem_Name,@Prem_PhysicalAddress,@Prem_PhoneNumber,@Town_ID)
     end
GO

In VB, I call it with the following code section:

Private Sub cmdAddTown_Click()
    Dim strTown_Name As String
    Dim strArea As String
    Dim pKey As Long
   
    On Error GoTo ErrorHandler
    Set rs = New Recordset
   
    strTown_Name = txtTown.Text
    strArea = cboAreaOffice.Text
    If strArea = "" Then
        MsgBox "You must specify the area office name from the drop-down menu before clicking add.", vbExclamation + vbOKOnly
        Exit Sub
    ElseIf strTown_Name = "" Then
        MsgBox "You must specify the Town name before clicking add.", vbExclamation + vbOKOnly
        Exit Sub
    Else
    With rs
        .Open "sp_get_PrimaryKeyArea" & " " & cboAreaOffice.Text, cn, adOpenDynamic, adLockReadOnly
    End With
        pKey = rs.Fields(0)
        cn.Execute "sp_Add_Town" & " " & strTown_Name & "," & pKey
        Set lstItem = lstTowns.ListItems.Add(1, , strTown_Name)
        cboTownPrem.AddItem strTown_Name
        txtTown.Text = ""
    End If
   
   
ErrorHandler:
    MsgBox Err.Description, vbExclamation + vbOKOnly
    Exit Sub
End Sub

This code gives me an Error number 0 and a blank Description.

What Error is this and how can I avoid such an error?

Pliz help