This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Your Question is not complete ....what is the name of your servlet is it ServletDemoOne??? or anything else ..
try to give give maximum information about the error....!!!
may be your application may not have been deployed properly....