This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori 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?