Thank you very very much for your help!!!
I go to playback–>properties–>advanced–>default format and I found this: canal 8, 24 bit, 48 KHz. so, If my audio files are in 44.1 KHz, I suppose thats the problem: My Audio Interface is working at 48 KHz when I playback the Wav file (that is in 44.1 KHz).
I tries to change from 48 KHz to 44.1 KHz but I can not change it. It seems that the box is fixed and I can not choose from 48 to 44.1.
Any idea??? Thanks!!!