Why is <taglib> giving me a problem in my web.xml?

Use this notation:

<jsp-config> 
        <taglib> 
               <taglib-uri>mytags</taglib-uri> 
               <taglib-location>/WEB-INF/jsp/mytaglib.tld</taglib-location> 
        </taglib> 
</jsp-config>

But I recommended to read this link. This tutorial will give you idea how to avoid declaring taglibs in web.xml in case of JSP 2.0

In the XSD referenced in your XML, it states that for complex type web-appType you can only have a choice of zero to many of the following elements:

<xsd:choice minOccurs="0" maxOccurs="unbounded">
  <xsd:group ref="javaee:descriptionGroup"/>
  <xsd:element name="distributable"
 type="javaee:emptyType"/>
  <xsd:element name="context-param"
 type="javaee:param-valueType">

  </xsd:element>
  <xsd:element name="filter"
 type="javaee:filterType"/>
  <xsd:element name="filter-mapping"
 type="javaee:filter-mappingType"/>
  <xsd:element name="listener"
 type="javaee:listenerType"/>
  <xsd:element name="servlet"
 type="javaee:servletType"/>
  <xsd:element name="servlet-mapping"
 type="javaee:servlet-mappingType"/>
  <xsd:element name="session-config"
 type="javaee:session-configType"/>
  <xsd:element name="mime-mapping"
 type="javaee:mime-mappingType"/>
  <xsd:element name="welcome-file-list"
 type="javaee:welcome-file-listType"/>
  <xsd:element name="error-page"
 type="javaee:error-pageType"/>
  <xsd:element name="jsp-config"
 type="javaee:jsp-configType"/>
  <xsd:element name="security-constraint"
 type="javaee:security-constraintType"/>
  <xsd:element name="login-config"
 type="javaee:login-configType"/>
  <xsd:element name="security-role"
 type="javaee:security-roleType"/>
  <xsd:group ref="javaee:jndiEnvironmentRefsGroup"/>
  <xsd:element name="message-destination"
 type="javaee:message-destinationType"/>
  <xsd:element name="locale-encoding-mapping-list"
 type="javaee:locale-encoding-mapping-listType"/>
</xsd:choice>

The taglib element is not referenced in the XSD at all.

From reading this link it would seem that you do not need to declare taglibs in the web-app document. Simply having the version="2.5" attribute means you can reference tags in your JSPs.