Some tag can not be contained in themselve. For ex, a FORM tag in a FORM tag.
This message can also appear due to previous errors in the order of tags.
Remove the nesting of tags.
Or correct the previous errors.
BAD <form action="action.jsp" name="form"> <form action="action2.jsp" name="form2"> </form> </form> GOOD <form action="action.jsp" name="form"> </form> <form action="action2.jsp" name="form2"> </form>
HTML specification: http://www.w3.org/TR/html4/