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.
Ninety-nine percent of the time this exception is caused by a simple spelling error. Are you absolutely sure that the type attribute in the <form-bean> stanza of your struts-config.xml file is spelled correctly and has the correct package name?
The next question I'd ask is: Did you remember to compile the class file and put it in WEB-INF/classes?
The third question I'd ask: Have you overridden or made non-public the default no arguments contstructor for the class?