How to keep connection alive?

[kalla ss]

I have craete a vb.net window application using soap web services. There is a module in my app. which runs every 2.5 sec (on timer tick event). On each tick event of timer this module call a web service method inside a background worker. It return some records in xml than this xml bind to datagridview. now the problem is sometime it shows :: The underlying connection was closed : A connection that was expected to be kept alive was closed.

how to solved it..