ho provato come mi hai detto ma ottengo sempre lo stesso risultato, ti posto il css in modo che mi puoi dire se è ok
codice:
body {
  margin:  0;
  padding: 15px;
}



#menuContainer {
  background-color: white;
  text-decoration: none;
  color: #666666;
  font-weight: bold;
  font-size: 10pt;
  font-family: Verdana, Arial, sans-serif;
  width: 10em;
  padding: 0px;
}

#menuContainer ul { 
  list-style-type: none;
  margin: 0;
  padding: 0;
}

#menuContainer li {
  background-color: #cacaca;
  border: 1px solid #1d374f;
  width: 10em;
  /* this is to make the submenus position relative to this li */
  position: relative; 
}

#menuContainer a {
  text-decoration: none;
  color: #666666;
  font-weight: bold;
  font-size: 10pt;
  font-family: Verdana, Arial, sans-serif;
}

#menuContainer li:hover {
  border: 1px solid #1d374f;   
  background-color: #abe1f4;
}

#menuContainer a:hover {
  color: #1d374f;
  border: 1px solid #1d374f;   
  background-color: #abe1f4;
}

#menuContainer ul ul {
  position: absolute;
  left: 10em;
  top: 0;
  visibility: hidden;
}

/*...........NEW..........*/


#menuContainer a ul {
  display: none;
}

#menuContainer a a ul {
  display: none;
}

#menuContainer a:hover ul {
  display: block;
}


#menuContainer a a:hover ul {
  display: block;
}

/*...........END NEW..........*/
grazie mille