Yes if you look at the page source of your forum and compare how the tables open you can see how the style class names are different than a normal vbulletin and why it doesnt work.
vbulletin uses forumhead etc.
Your one special style has different class names like vbs_forumhead. You can try editing that custom style and make the contents of the forumhead class match that which your vbs_forumhead class has by chance just a suggestion.