Correzione a main.jsp:

"main.jsp":
...

<%@ include file="menu.jsp" %>
...
<% int intPercorso=request.getParameter("perc");
if (intPercorso==1) {%>

<%@ include file= "pagina1.jsp" %>
<%}else {%>
<%@ include file= "pagina2.jsp" %>
<%}%>

...