"The specified user does not exist" error message when you try to use the DSMOD command to add a user from one forest to a group in another forest in Windows Server 2003

for each strArg in wscript.Arguments.Named
	strValue = wscript.Arguments.Named.Item(strArg)
	select case lcase(strArg)
		case "g" ' logging
			groupDN = strValue
		case "u"
			userDN = strValue
		case "?","help","h"
			wscript.echo "cscript /nologo " & wscript.scriptname & " [/g:groupDN] [/u:userDN]"
			wscript.quit			
	end select
next

set oProv = GetObject("LDAP:")
set oGroup = oProv.OpenDSObject("LDAP://" & groupDN, vbnullstring, vbnullstring, 1)
set oUser = oProv.OpenDSobject("LDAP://" & userDN, vbnullstring, vbnullstring, 1)

oValue = oUser.Get("objectSid")
oString = OctetString2String(oValue)
oGroup.PutEx 3, "member", Array("<Sid=" & oString & ">")
oGroup.SetInfo

Function OctetString2String(byVal OctetStr)
dim result
dim j, loByte, hiByte

    result = ""
    for j = lbound(OctetStr) to ubound(OctetStr)
        hiByte = ascb(midb(OctetStr,j+1,1))
        loByte = hiByte mod 16
        hiByte = hiByte \ 16
        result = result & hex(hiByte) & hex(loByte)
    next

    OctetString2String = result
End Function