I was in the battle tower. A previous match ago a Pokemon lowered my accuracy. Then my body slams kept missing after that battle. Body slam has a 100% accuracy.
There are two types of move you may be talking about. Regular moves like Scratch, Ember and so on have 100% accuracy but are affected by many things: - accuracy-reducing moves like Sand-attack - evasive moves like Double Team - some two-turn moves like Dig or Fly (i.e. when the Pokemon has left the battlefield attacking moves will miss) - hold-items such as BrightPowder (lowers the foe's accuracy) - fog weather condition
There are also moves that cannot miss, like Swift. We call those "infinite accuracy" moves since the accuracy cannot be reduced by the things listed above.
http://pokemondb.net/pokebase/654/how-does-a-move-with-100%25-accuracy-miss
there is the chance that your opponent was holding brightpowder.