Gaby,
could you please send me a copy of your project so I can take a look at it? If you can also include your modified command, that would be great.
Please let me know what version of TM you're using...
In the meantime, please take a look at the MTASC Help (Bundles » ActionScript » MTASC » MTASC Help), section 1.3: Debugging, just in case there's some obvious thing you're missing (happens to me all the time : )
The XTrace debugging feature may be removed from the bundle sometime in the future, as you can get pretty much the same results by using Console.app. Take a look at this post http://bomberstudios.com/2007/03/14/how-to-use-consoleapp-for-flash-debugging/ for more information about this (and maybe some more insights on your problems with XTrace)
Hope it helps...