I accidentally missed your previous message. Sorry for the late reply, I hope you understand I have a life outside of the forums, and don't stay here 24/7.
For static encounters (such as legendaries) in Generation 3, there's only 6 PIDs that can yield perfect IVs.
Those natures are locked, too. The 6 natures in the table above is Modest, Docile, Modest, Timid, Calm, and Modest.
You likely just think that the nature needs to be Modest, because it has a 50% chance of showing up when trying to obtain a Gen 3 legendary with perfect IVs.
This is what I was talking about in my initial reply: "trying to change the IVs/PID/Shininess could cause illegality, as the information is 'calculated based on a formula'"
According to the formula, the PID of 685011A9, with all IVs at 31, can only have nature Modest.
Correct me if I am wrong, however I believe you just changed your nature here (seen in picture below).
That caused the Groudon's PID to change, and made the Groudon illegal. (and this is what the error 無効: エンカウントタイプと性格値が一致しません which in this case means: the IVs selected doesn't match what the formula would have generated.)
For Generation 3, changing the nature there can cause legality errors. Keep in mind it is still possible to make the Groudon legal, but it will involve changing the IVs (I will show the fix further down).
Explanation on "the formula" I mentioned above.
Example of me trying to fix your Groudon with the new PID:
Extra information:
Eggs have a different formula from static encounters (such as Groudon), hence why Nature isn't an issue.