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.
This is a very generic error that tells us nothing about what is happening. When this error occurs, your application server is logging it in its System Out log file. Please find the error in the log and post that error, along with the first few lines of the stack trace. Also, give us a brief description of the page and any other information you think might be relevant to the error.