Audio Fade - please help

Hello, I would like please you to help me with very simple problem. I have model 410 and need play only one mp3 audio file in loop. After press button fade only volume. 3 or 4 seconds fade out to 0, after press the same button again volume fade up to 100 the same time 3 or 4 seconds. I try write function to script but still i have error: for fade out LET Volume1 = 100 LET VolStep = 2 LET VolStepTime = 40 setVolume1: FOR volume = volume TO volume1 STEP -VolStep audio.SetVolume(volume) sleep(20) NEXT volume return for fade up the same function but opposite. I try all scripts but i am still unsuccessful. Pavel