Custom MDT Script Failing

I am attempting to assign a computer to a security group within a task sequence during the System Restore phase.

I have customized the deployment wizard to add a drop-down list to the ComputerName portion of the deployment wizard. This drop-down list has a small number of selections that have been manually assigned values that correspond to the guid of the security groups that the computer may be assigned to. This value is then assigned to a new MDT Property called "DomainUpdateGroup". When the summary page is displayed, this value is correctly populated into the Variables.dat. Then during the system restore phase of the deployment, I have created a "Run Command Line" step that calls the script from the scripts folder of the deployment share (%scriptroot%). Because the task that is being performed requires Active Directory permissions, the script is being run as an account with the permissions to make changes to computer objects.

<job id="Z-Sample"><script language="VBScript" src="ZTIUtility.vbs"/><script language="VBScript">
		' //***************************************************************************
		' // ***** Script Header *****
		' //
		' // Solution: Solution Accelerator for Microsoft Deployment
		' // File: Z-Sample.wsf
		' //
		' // Purpose: Template
		' //
		' // Usage: cscript Z-Sample.wsf [/debug:true]
		' //
		' // Customer Build Version: 1.0.0
		' // Customer Script Version: 1.0.0
		' // Customer History:
		' //
		' // ***** End Header *****
		' //***************************************************************************
		'//----------------------------------------------------------------------------
		'//
		'// Global constant and variable declarations
		'//
		'//----------------------------------------------------------------------------
		Option Explicit
		Dim iRetVal
		'//----------------------------------------------------------------------------
		'// End declarations
		'//----------------------------------------------------------------------------
		'//----------------------------------------------------------------------------
		'// Main routine
		'//----------------------------------------------------------------------------
		On Error Resume Next
		iRetVal = ZTIProcess
		ProcessResults iRetVal
		On Error Goto 0
		'//---------------------------------------------------------------------------
		'//
		'// Function: ZTIProcess()
		'//
		'// Input: None
		'//
		'// Return: Success - 0
		'// Failure - non-zero
		'//
		'// Purpose: Perform main ZTI processing
		'//
		'//---------------------------------------------------------------------------
		Function ZTIProcess()
			iRetVal = Success
			ZTIProcess = iRetval
			'!!!!!!!!!!!   INSERT YOUR CODE HERE   !!!!!!!!!!!!
			Dim strUpdateGroup, strComputerCN, UpdateGroupMember, arrDomainUpdateGroupMembers
			Set oSystemInfo = CreateObject("ADSystemInfo")		

			strUpdateGroup = oEnvironment.Item("DomainUpdateGroup") 'value here is the guid of the security group
			strComputerCN = oSystemInfo.ComputerName 'returns the distinguished name of computer			

			'bind to Update Group object to add computer to security group
			Set oDomainUpdateGroup= getObject("LDAP://domain/<" & strUpdateGroup & ">") 'format string for LDAP query using a guid binding
			oDomainUpdateGroup.getInfo

			arrDomainUpdateGroupMembers = oDomainUpdateGroup.getEx("member")

			'validate group membership and add to selected group if not a member
			For Each UpdateGroupMember in arrDomainUpdateGroupMembers
				If UpdateGroupMember = strComputerCN Then
					'computer is already a member of this security group
					Exit For
				Else
					'add computer object to security group
					oDomainUpdateGroup.Add("LDAP://" & strComputerCN)
					oDomainUpdateGroup.setInfo
					Exit For
				End If
			Next 
		End Function</script></job>

The wsf file was placed into the mdt scripting template. The coding above (less the MDT templating information) will run if executed from a command line that was started in the run as context of the same user designated in the task sequence.

When this script is called from the task sequence it fails and returns an error (500) Variable is undefined. Unable to create WebService class. Unless I am missing something in my script I don't have an undeclared variable and I don't think I am instantiating a web service class either.

Any ideas as to why this might be occurring?