Basically when editing your menu, you must have the item activated (using the left checkbox) in order to activate the item on your splash/frame page (using the right checkbox). This would enable the item to appear in both the splash/frame menu as well as your main menu.
The system was designed to work this way, as the splash/frame menu items originally were used simply as shortcuts to the most popular menu items.
There is a way around this however. To activate a splash/frame menu item without having it active on the main menu, do the following:
1. Login to your website admin.
2. Click on Navigation Menu.
3. Click on Add Category.
4. Add a category, for example "Splash Items".
5. Click to Add the Category.
6. You will see the category you added on the list.
7. Uncheck the Active checkbox to make the category inactive.
8. Click Save Changes.
9. Click to Return to Main Menu.
10. Click on Navigation Menu.
11. Click on Edit Navigation Menu.
12. Find the item you want to appear on ONLY the splash/frame page. Check the both the left and right checkbox for that item.
13. For that item, assign it to the category you added, in this case "Splash Items".
14. Click Save Changes.
Your menu item should now only appear in the splash/frame page menu and not in the main menu. This will only work when assigning that menu item to an inactive category. If you assign it to an active category then it will appear on both menus.