Ulysses' men betrayed him by opening the leather bag witch was full with 'winds' that Aeolus gave. Poseidon made this (the betrayal) happen, because he made the sound of coins in the leather bag and it made the men suspicious. After all, Ulysses warned the men not to touch the leather bag, but the men had betrayed him. Ulysses was apparently asleep while that happened seeing that he didn't sleep for nine days and nine nights.