Thats strange...
the problems you get are normal, IF
you should use the
public CustomTag extends TagSupport {}
it uses the doEndTag() and doStartTag(), so you must use them
but you are using the
public class CustomTag extends SimpleTagSupport
...im not familiar with the SimpleTagSupport, but i see that your doTag() should be enough...
The way i see it, you get errors like it would come from Tagsupport, not from SimpleTagSupport...
of course...it could be something in your tld not being right...