Actually I am very new to tomcat and eclipse. my applications is get running fine when I not use the option reload in the tomcat. If I click the folder directly without using the reload button everything is going fine. while I use the reload button
Does your deployment descriptor (web.xml) have a servlet entry with a class attribute that has a value of cart.servlet.Welcome.
If so, and you don't have that class in your project anymore, then when you start the app (if you have the load-on-startup attribute set) then the container will look for that class and throw the exception when it can't find it.