VB active directory logon script

Hi,

Please could someone take a look at this logon script for me.  It is basically a logon script to set a users printer based on active directory group membership.
The script seems to run fine but does not do the requested action by mapping a printer when I add my self to any of the groups.  No errors are reported at all.  I added a wscript.echo command to the beginning of the subroutine, however this comment is never echoed suggesting my subroutine sections are not working.
I know this is a big ask as you need to work this script out; I would very much appreciate the help so please could someone tell me where I have gone wrong?

See script bellow
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Option explicit
'On error resume next
Dim wshNet
Dim ADSysInfo
Dim CurrentUser
Dim GroupMember
Dim strGroups
Dim a, b, c
Dim PCompPrinter
Dim PRoomPrinter
Dim ReceptionPrinter
Const PComp = "CN=Post Completion"
Const PRoom = "cn=Post Room"
Const Reception = "cn=Reception"

PCompPrinter = "\\Cs1\nclepostcomp"
PRoomPrinter = "\\Cs1\NCLE - Epson C3000 Colour Laser"
ReceptionPrinter = "\\Cs1\NCLE - RECEPTION HP LaserJet 1100"
Set wshNet = CreateObject("WScript.Network")
Set ADSysInfo = CreateObject("ADSystemInfo")
Set CurrentUser = GetObject("LDAP://" _
    & ADSysInfo.UserName)
strGroups = LCase(Join(CurrentUser.MemberOf))

Select Case GroupMember
        Case a = Instr(strGroups, PComp)
      PCompsub
        Case b = Instr(strGroups, PRoom)
      PRoomsub
        Case c = Instr(strGroups, Reception)
      Receptionsub
End Select

Sub PCompsub
wshNet.AddWindowsPrinterConnection PCompPrinter
wshNet.SetDefaultPrinter PCompPrinter
End Sub

Sub PRoomsub
wshNet.AddWindowsPrinterConnection PRoomPrinter
wshNet.SetDefaultPrinter PRoomPrinter
End Sub

Sub Receptionsub
wshNet.AddWindowsPrinterConnection ReceptionPrinter
wshNet.SetDefaultPrinter ReceptionPrinter
End Sub

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