No limit on buttons allowed for basic menu in DVD Wizard
From my research it appears that a single DVD menu can't support more than 36 buttons and no more than 18 buttons if in widescreen. The DVD Wizard doesn't currently provide any warning that the extra buttons won't work - they simply aren't selectable in the finished DVD. Disabling the UI for adding buttons when the limit is reached would be ideal, perhaps with an error message to indicate the issue.