Main Menu Error : duplicate id in sublevels

[rvm]

Hi all,
first a great thanks for your effort and now the bad, I try to create a dropdown menu using normal joomla(a8e) structure but it fail validation cause id of are duplicated, so remember that I dont change "main menu" from it default state (vertical) to flat list, but, in this vay there's no expansion or sublevel at all, I try to use horizontal, but in this mode a8e push table(!) even without sublevel.
It's possible to use normal a8e menu with sublevels without hack the core?

Sorry for my bad english, and thanks again!

rt