Tomcat not executing Servlets service() method

I have web applications in Tomcat 5.5 .I have a default configuration for tomcat

I hit URL to various servlets , these are normal servlets , and get a response as expect开发者_开发知识库ed ,

but sometimes i get response and nothing in it.It gives me blank response

I tried to debugged same and i found that service() [doGet / doPost] of particular servlet is not being executed.

I checked access logs of Tomcat i found request is hitting atleast to that servlet

192.168.0.116 - - [14/Oct/2011:11:40:31 +0530] "GET /MyApp/myServlet HTTP/1.1" 200 -

Why container not executing the service()?