Not sure if the right place to post. But some Pokemon that can only learn Avalanche in Gen IV by way of TM are throwing legality errors for that move. This happens with Blastoise, Nidoqueen, Aggron and likely others. However at the same time, this doesn't happen with other Pokemon that can only learn Avalanche through Gen IV TM, such as Kangeskhan.

http://www.serebii.net/pokedex-xy/306.shtml - See Transfer Only Moves
(side note: no idea why this doesn't throw an encounter PID legality error, considering I didn't generate a valid gen IV PID for its IVs/Nature)
http://www.serebii.net/pokedex-xy/115.shtml - See Transfer Only Moves
Try changing Met Level to 100
You shouldn't suspect a 'bug' if the pkm was originally hacked ;)
Haha oh that was so dumb of me. Met level had to be 100. I guess PkHex has changed a lot since I last used it. >_< I still don't know why that Kangeskhan showed as legal though. Considering it wasn't set to level 100 and I hadn't generated a Gen IV PID (which I usually need to do with Game Origin Gen 3/4 Pokemon. Oh well. Keep up the great work. :D
The last line of the popup tells you why: there is no PIDIV relationship for Gen4 eggs, thus there is no chance for a "PIDIV method mismatch". Still needs to have the correct nature (PID%25) if transferred onward.
Most helpful comment
Try changing Met Level to 100