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.
You need to read the exception. It says the error occurred in your code at line #91 of Client.java. You're doing an RMI lookup() there, and the thing you are looking up is not found. You probably have the wrong name for the remote object. Find out what name the remote object used when it registered itself, and verify that it actually does so.