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.
Not sure off hand -- I don't see anything wrong in the code you posted. You should check the session in a debugger to make sure that the value is actually removed when it gets back to the JSP. Note that, if you use a useBean tag at the top, it automatically creates the bean for you, which may be the problem.