Recently, I came across the following JBoss -> GlassFish migration issue involving taglib-location in web.xml. Here is how I dealt with it.

In a web-application's web.xml, <jsp-config> element can be used to provide configuration information for JSP files. The following fragment works on JBoss 4.3 (or so it was indicated to me)

   <jsp-config>
     <taglib>
       <taglib-uri>example-html.tld</taglib-uri> 
       <taglib-location>WEB-INF/example-html.tld</taglib-location> 
     </taglib>
   </jsp-config>

But on GlassFish v2, the web application's deployment to failed with the following exception in GlassFish server.log file.

     javax.servlet.ServletException: PWC3039: Invalid TLD resource path /WEB-INF/WEB-INF/example-html.tld

To fix error, prefix a / to taglib-location

   <jsp-config>
     <taglib>
      <taglib-uri>example-html.tld</taglib-uri>
      <taglib-location>/WEB-INF/example-html.tld</taglib-location> 
     </taglib>	
   </jsp-config>

So is a leading / for taglib-location *required* ? After browsing through JSP & Servlet specs and xml schema files I interpreted that a / is not required but recommended. But I will defer to the Servlet spec lead for a more definite answer.