A couple things I see:
1) In your "SpryMenuBarHorizontal.css" file
under "ul.MenuBarHorizontal ul.MenuBarSubmenuVisible"
there's a line that says "left: -1px;"
change that to "left: auto;"
2) You have both a "SpryMenuBarHorizontal.css" file and a "SpryMenuBarVertical.css" file being linked to. You should remove the reference to the "SpryMenuBarVertical.css" in your html doc.
Abraham