java.lang.NoClassDefFoundError: javax/servlet/jsp/el/VariableResolve

I am getting a following error only when I use a c:set in my jsp.  All the other c tags work no problem.
java.lang.NoClassDefFoundError: javax/servlet/jsp/el/VariableResolver

            at java.lang.Class.getDeclaredMethods0(Native Method)

            at java.lang.Class.privateGetDeclaredMethods(Class.java:1681)

            at java.lang.Class.getDeclaredMethods(Class.java:1144)

            at java.beans.Introspector$1.run(Introspector.java:1126)

            at java.security.AccessController.doPrivileged(Native Method)

            at java.beans.Introspector.getPublicDeclaredMethods(Introspector.java:1124)

            at java.beans.Introspector.getTargetMethodInfo(Introspector.java:989)

            at java.beans.Introspector.getBeanInfo(Introspector.java:370)

            at java.beans.Introspector.getBeanInfo(Introspector.java:144)

            at java.beans.Introspector.getBeanInfo(Introspector.java:205)

            at java.beans.Introspector.<init>(Introspector.java:351)

            at java.beans.Introspector.getBeanInfo(Introspector.java:144)

            at org.apache.jasper.compiler.TagCache.setTagHandlerClass(TagCache.java:116)

            at org.apache.jasper.compiler.TagBeginGenerator.init(TagBeginGenerator.java:150)

            at org.apache.jasper.compiler.JspParseEventListener$GeneratorWrapper.init(JspParseEventListener.java:866)

            at org.apache.jasper.compiler.JspParseEventListener.addGenerator(JspParseEventListener.java:153)

            at org.apache.jasper.compiler.JspParseEventListener.handleTagBegin(JspParseEventListener.java:1076)

            at org.apache.jasper.compiler.DelegatingListener.handleTagBegin(DelegatingListener.java:221)

            at org.apache.jasper.compiler.DelegatingListener.handleTagBegin(DelegatingListener.java:216)

            at org.apache.jasper.compiler.Parser$Tag.accept(Parser.java:852)

            at org.apache.jasper.compiler.Parser.parse(Parser.java:1157)

            at org.apache.jasper.compiler.Parser.parse(Parser.java:1115)

My c library is declared like this: <%@ taglib uri="/WEB-INF/c.tld" prefix="c"%>
and, just in case here's the first few lines of that c.tld file, so you know which one it is:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib
  PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
  "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
  <tlib-version>1.0</tlib-version>
  <jsp-version>1.2</jsp-version>
  <short-name>c</short-name>
  <uri>http://java.sun.com/jstl/core</uri>
  <display-name>JSTL core</display-name>
  <description>JSTL 1.0 core library</description>