why cant i register ceratin pokemon in collosium?

[bman14]

i thought you could register pokemon like metagross and milotic in the collosium battle mode? but when i tried to register them, it said "inadmisible pokemon cant be entered." what the heck does that mean and how can i fix it?

 

[TRJessie579]

I believe in Battle Mode, each of your Pokemon must be carrying a different hold item. If your Metagross or Milotic is holding something another one of your Pokemon is also holding, it may not let you register it.

 

[DJ-Will]

Did you shark them? Colosseum will recognize hacked Pokemon.

 

[ZNtelle]

There's also the possibility that you have an illegit version of Colosseum, though I think the two prior posts contain more likely scenarios than what I posted.