Playing a mp3 problem with mpg123

Asterisk 1.4.7 installed from source on fedora 7
I followed most of the instructions of the O’Reilly book
mpg123 installed from source with the latest stable version 0.66

my extension§.conf relevant part:

exten => 123,1,Answer() exten => 123,2,MP3Player(Thosedancing.mp3)

This is the message displayed on the Asterisk console in verbosity mode 3 :

I tried to copy/paste the error message in Google but I’ve got no results so I ask the question here. I hope it is not judged impolite. Thanks for your support.

edit: I noticed that I should use this code (without the .mp3) but the result is the same :

exten => 123,1,Answer() exten => 123,2,MP3Player(Thosedancing)

edit: my mp3 file is in the same directory as all the .gsm files (the sound directory)