Spread your party members around, with your tanks and summoned creatures (which you will use as fodder) within melee range around the dragon. Don't have them all clustered together as one wing buffet will knock them all away. Lower-armored melee fighters should be behind the dragon. Ranged attackers and spellcasters should be well away from the dragon's breath weapon or buffeting attacks.
The first arcane spells you should cast should be: Lower Resistance (twice preferably), then Greater Malison, then a disabling spell like Remove Magic to get rid of his stoneskin. If you have a druid or ranger that can cast Summon Insects or Insect Swarm it will prevent him from casting spells. Just hammer away. Try casting a lot of instant kill spells after you've cast Greater Malison.
Good luck!
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