If you are asking for violations of the War Powers Act, Ronald Reagan did not get Congressional approval (and rightly so) before invading Grenada. He basically ignored the Act because it was unconstitutional. The difference with Obama is that he actually cited the War Powers Act in his electronic notification to Congress (which was actually received after the 48-hr deadline).
Reagan did not acknowledge the legitimacy of the War Powers Act, and acted accordingly. Obama does acknowledge the legitimacy of the War Powers Act, and by default is bound to honor it - not grounded on legality but by integrity.
Grenada wasn’t the same situation or similar military action.