exception in MessageTag.doStartTag()

[RoleModel Software]

We're just starting to learn about Struts. We have downloaded the code (and binaries) (v.b3) for struts-example. The binaries run fine, and we get the expected output. When we try to set up the source version, though, we get the following error:    javax.servlet.jsp.JspException java.lang.Throwable(java.lang.String) java.lang.Exception(java.lang.String) javax.servlet.jsp.JspException(java.lang.String) int org.apache.struts.taglib.bean.MessageTag.doStartTag() void _0002findex_0002ejspindex_jsp_0._jspService(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)...   Can anybody give us a clue about what's going on? As far as we can tell, we've got everything configured properly, but we're guessing we made a mistake somewhere.   Thanks.   Michael and Roy