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.
Please remove any xerces related jar that you have added into the existing JBoss. JBoss 5.1 already contains xerces jars and you don't need to add those jars again which might be old. I had faced the same problem while upgrading from JBoss 4.2 to JBoss 5.1.