I haven't found the solution yet....
follows my playonlinux output:
raphael@DeathStar:~ $ playonlinux
[main] Message: PlayOnLinux (4.1.7) is starting
[clean_tmp] Message: Cleaning temp directory
[Check_OpenGL] Message: 32bits direct rendering is enabled
[Check_OpenGL] Message: 64bits direct rendering is enabled
[main] Message: Filesystem is compatible
Error: Unable to reserve a valid port
[maj_check] Message: List is up to date
[xcb] Unknown request in queue while dequeuing
[xcb] Most likely this is a multi-threaded client and XInitThreads has not been called
[xcb] Aborting, sorry about that.
python: xcb_io.c:178: dequeue_pending_request: Assertion `!xcb_xlib_unknown_req_in_deq' failed.
/usr/share/playonlinux/playonlinux: line 141: 23105 Aborted "$PythonBin" mainwindow.py "$@"
/usr/share/playonlinux/playonlinux: line 138: python2.6: command not found