Could you add a few more details? If you want to add items, simply go to Tools > Items and click on any item slot twice (not rapidly, though) to change its kind.
http://en.pokemon-gl.com/#/information/517
I'd export the PGF file in Pokégen. Next time I go to Wal-Mart, I'd probably ask about the Sinnoh starter Pokémon.
Use Pokémon Studio Injector for the Pokéstar Studios Pokémon, as they lock-up the game upon capture. As of now there is no way of Generating Action Replay codes to inject these Pokémon.
If you can type the code carefully, hopefully it should be fine. Sorry I keep implying that Pokégen codes won't work for international Black and White 2, at least on emulators I tried a US Black 2 and French White 2.
I only managed to do it with someone at GameFAQs once. It required me to make Tornadus have the same OT/ID/SID as the trainer of the player with a legitimate Reveal Glass in order to get the Forme Change to work.
Maybe you could send me a pkm file or Action Replay code of Thundurus and I'll inject it into my game, obtain a working Reveal Glass, and we could trade if you can access Wi-Fi.
The hack checks on the GTS are terrible. If Pokégen were to create only GTS-legal Pokémon, one would have to run an analysis on what meets the GTS standards and what doesn't.
That never happened to me. Try backing up your save file or use a different C-Gear Skin to see if it'll work. I'd also make sure that I've progressed far enough into the game to have the C-Gear.
Do you have the anti-piracy patched? That could be one of the problems. Also, Pokégen hasn't been updated to generate codes for the US versions of Black 2 and White 2.