A Spinarak I RNG'd in SS/transferred to Gen V comes up as having an illegal combination of Egg Moves.
https://www.pokecheck.org/?p=detail&uid=2382257
The combination is actually possible though, using a male Beedrill from (Baton Pass), two Heart Scales to reteach it Pursuit and Toxic Spikes and then leveling a bit/using a TM to pass down Poison Jab before breeding with a female Ariados (also with Poison Jab).
I'm not worried about it or anything (I'm guessing it's just because it involves an Pokemon or something like that) but I thought I should point it out in case it might be helpful.