Error with Shiny Squirtle Line

[Fehish]

I recently hatched a shiny Squirtle for my girlfriend, but every time I try to view it in the "Pokémon" tab, I get an error: "Incorrect bkGD chunk index value", then two lines down it says "CNxFile Object: Graphics/Battlers/007s.png". I raised it all the way to a Blastoise and got the same error message, only the 007 changed to 008 and 009 upon evolving. It doesn't crash the game, but it pops up every time, and I'm unsure how to fix it.