It's because the map maker has used a map protector to encrypt the map so others can't see it. This is done because many map-makers are sick and tired of n00bs taking their hard work, changing 1 thing and then sticking their names on it. The downside to this is that people who genuinely just want to see how things are done are unable to do so.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.