Getting Error while deploying simple servlet

[henpat123]

Hi,
I am new to weblogic 8.1.I wrote a simple servlet and followed all the instruction to create a .war files and web.xml and weblogic.xml. When I am trying to deploy the Web Application module from the Weblogic 8.1 console, I select the WAR file, and I get this Error:

Exception:weblogic.management.ApplicationException: Prepare failed. Task Id = 4 Module: EinsWebAppModule Error: [HTTP:101179][HTTP] Error occurred while parsing descriptor in Web application "C:\bea\user_projects\domains\MyDomain\applications\MyWebAppModule.war" [Path="C:\bea\user_projects\domains\MyDomain\applications", URI="MyWebAppModule.war" weblogic.xml.dom.DOMProcessingException: Neither principal-names nor externally-defined element specified for security-role-assignment at weblogic.servlet.internal.dd.SecurityRoleAssignment.<init>(SecurityRoleAssignment.java:73) at weblogic.servlet.internal.dd.WLWebAppDescriptor.<init>(WLWebAppDescriptor.java:147) at weblogic.servlet.internal.dd.DescriptorLoader.initializeWebLogicXml(DescriptorLoader.java:742) at weblogic.servlet.internal.dd.DescriptorLoader.<init>(DescriptorLoader.java:303) at weblogic.servlet.internal.dd.DescriptorLoader.<init>(DescriptorLoader.java:235) at weblogic.servlet.internal.WebAppModule.loadDescriptor(WebAppModule.java:520) at weblogic.j2ee.J2EEApplicationContainer.loadDescriptors(J2EEApplicationContainer.java:1398) at weblogic.j2ee.J2EEApplicationContainer.prepare......
....
and more

Can Somebody tell me what I could be missing?

henry