This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Sounds like a classpath issue. A nice feature here at JavaRanch is the ability to search past conversations for lots of valuable information. If you try a quick search on this forum for "NoClassDefFoundError" in the subject line, you'll find many past conversations on this topic and the corresponding solutions. The search page link is at the top right of this page. Any luck?