IIS 7.5 W3WP.exe service restarted automatically and sometimes failed to response to a ping.

Hi All, The .Net 3.5 worker process for our application keeps crashing. We see the following error message in event log. A process serving application pool 'WebApplication' failed to respond to a ping. The process id was '7344'. The .net application exposes web services. The client application of a web service which disappears as a result of this crash experiences the following exception: System.Net.WebException: The underlying connection was closed: An unexpected error occurred on a receive. ---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host    at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)    at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 ...