Ritu,

Without seeing your entire script it is a little difficult to diagnose.  A couple of thoughts; first, your variable 'NumRecords' is an integer but the value you are passing to the global token 'NumVouchRecUpd' is a string.  Secondly, are you sure you are properly instantiating the 'NumRecords' variable as an integer and assigning a good value to it? 

Here is a quick code snippet that works on my system (Workflow 9.02);

       Protected Overrides Sub Execute()
            Dim numRecords As Integer

            numRecords = 256

            SetTokenValue("NumVouchRecUpd", numRecords)

        End Sub

Notice that the value I am assigning to the 'NumVouchRecUpd' token is the integer value not a string. 

When I use the code above in a script activity I have a token available from the 'SDK Script' activity named 'NumVouchRecUpd' which can be referenced by other activities.

Let me know if that helps.