I just tried to trade for the first time in the GTS with my new Pokemon Platinum game. Here's what happened:
I searched for an Altaria between 41 and 50, I got one hit, and it was shiny! I was so excited because they were asking for a male Leafeon, and I had one! But, I tried to trade it, and it was greyed out. I tried taking it out of my party, taking off its item, nothing worked. So, I did some trolling on other pokemon forums, and it appears that you can't see when people ask for pokemon of a certain level in Platinum? So it was grey because they asked for a Leafeon of some level different than mine, and I had no way of knowing that.
Is this the case? If so, is this a known bug, or is this intentional? Because if it is, that makes it nearly impossible to use.