your problem must be linked to that error because the add-ons button must be there on the characters selection page, bottom corner left exactly. If I remember the add-on button does not display if 0 addons are detected, are you sure you have dirs that loooks like this with auctioneer?
Code:
D:\Games\World of Warcraft\Interface\AddOns\Auc-Advanced\*all files
D:\Games\World of Warcraft\Interface\AddOns\EnhTooltip\*all files
D:\Games\World of Warcraft\Interface\AddOns\Stubby\*all files