Webservice Issue - Server was unable to process request

Hi,
I am using VS 2012, C#, ASP.NET.
I am invoking a webservice, which returns the data for almost 70% of the time.
At times, I am getting the error:
Exception: Server was unable to process request. ---> The server is not operational.
Stack Trace:
at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall) at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)
The code block which initiates the webservice is wrapped in a try catch block.
How to fix this? Please let me know, if any more information is needed.
Thanks