I think you've given us either the wrong stats or the wrong IV and EV spread which may be something to do with why the Pokemon isn't usable. A Chansey with Sassy nature and full IVs with the EV spread you gave us has the following stats (that differ a fair bit from yours) HP:704, ATK:46, DEF:47, SATK:106, SDEF:339, Speed:122.
So most notably, your ATK stat and SDEF stat is far off what it should be and the speed and SATK stat is marginally smaller/larger than what it should be. The SATK must have some form of EV investment also which seems odd. It may not explain your problem but it should help improve your set as some values are clearly lacking in some places.