Are you trying to click both pieces into place before submitting your move? If so there's no need, just move the king to the appropriate square and the site will do the rest.
Originally posted by AnaMariaBlondAngel King moved to G8 ok so far but when rook called to move F8 then King switches back to E8 ! What is up here ?! Thank you asap !
Move the king and than click move.....It knows that you are trying to castle and will finish the move for you.