Tim, please remember that there are some people that still refer to the default interface as "vanilla". But, I don't know if that's the case here.
The o.p. could be talking about the classic (the "new" game(?)) interface, also.
@nonexistentx_x: Help will not be provided for private server players, as WoWInterface is a Blizzard official fan site.
There is more to the warning, but I just can't remember what it is. Sorry.