javadoc NullPointerException

Can anyone point me in the right direction on this javadoc error?

Thanks!

Standard Doclet version 1.6.0_10
Building tree for all the packages and classes...
java.lang.NullPointerException
at com.sun.tools.javadoc.TypeMaker.getType(TypeMaker. java:67)
at com.sun.tools.javadoc.TypeMaker.getType(TypeMaker. java:29)
at com.sun.tools.javadoc.ClassDocImpl.superclassType( ClassDocImpl.java:441)
at com.sun.tools.doclets.internal.toolkit.util.Util.g etAllInterfaces(Util.java:386)
at com.sun.tools.doclets.internal.toolkit.util.Util.g etAllInterfaces(Util.java:424)
at com.sun.tools.doclets.internal.toolkit.util.ClassT ree.processType(ClassTree.java:162)
at com.sun.tools.doclets.internal.toolkit.util.ClassT ree.buildTree(ClassTree.java:114)
at com.sun.tools.doclets.internal.toolkit.util.ClassT ree.<init>(ClassTree.java:73)
at com.sun.tools.doclets.internal.toolkit.AbstractDoc let.startGeneration(AbstractDoclet.java:104)
at com.sun.tools.doclets.internal.toolkit.AbstractDoc let.start(AbstractDoclet.java:64)
at com.sun.tools.doclets.formats.html.HtmlDoclet.star t(HtmlDoclet.java:42)
at com.sun.tools.doclets.standard.Standard.start(Stan dard.java:23)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Native MethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(De legatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.sun.tools.javadoc.DocletInvoker.invoke(DocletI nvoker.java:269)
at com.sun.tools.javadoc.DocletInvoker.start(DocletIn voker.java:143)
at com.sun.tools.javadoc.Start.parseAndExecute(Start. java:340)
at com.sun.tools.javadoc.Start.begin(Start.java:128)
at com.sun.tools.javadoc.Main.execute(Main.java:41)
at com.sun.tools.javadoc.Main.main(Main.java:31)
2 warnings