I get the following exception when i request the same JSP after a long time has elapsed. Restarting the server resolves the issue. I wanted to know when can this occur.
The duration between two requests is usually around 24 hours. Does that have anything to do with it? Or is it a memory issue?
There's your problem. If you're using Tomcat, go to the main Tomcat folder, then sub folder work\Catalina\localhost\XXX\org\apache\jsp with XXX being the web application's name. You may need to replace localhost with the actual host if you're using a different one.
Inside look for file index_jsp.java. This file is generated automatically from your index.jsp file. Look for line 169; something on that line may be null at times. You should recognize this line as one from your original index.jsp file. That's where you should look at.