First, re-read your post, please - you give no real information about what you are doing. When a crash occurs you can either panic (the easy route) or recognize you are more clever than the computer and you can, if relaxed and systematic, solve the problem.

First you say:

Within ableton live, usb midi was working perfectly but when i switched to the usb audio driver steinberg, first ableton live could not use the driver.

There is no such thing as the "Steinberg driver". We assume you are referring to the "Yamaha Steinberg USB driver" which is a dual driver that can independently be set for MIDI communication and Audio communication.

From this we can conclude, that since USB-MIDI "was working perfectly" that the Yamaha Steinberg USB driver is installed and working.

After a restart of ableton i could swtch to steinberg driver but montage start to freeze. I had to restart the montage and it showed a white screen during a second before the usual start screen.. I am afraid to try again. Is it ableton issue or a conflict with the inboard soundcard rme ? Is this happen to somebody ?

From this we are going to assume, you are attempting to configure Audio (on what computer, we don't know, on what operating system, again we don't know)

Then you briefly mention another audio interface: "rme ?" - you cannot use the Yamaha Steinberg USB driver to connect the Montage to an "rme" audio interface. If you are using an rme audio interface, please use the driver they recommend and connect the main Left and Right outputs of the Montage to that audio interface.

If you require more help, please provide details (that means make and model of the audio interface you wish to use if not using the Montage as your audio interface, the driver complete name and version number, computer type, computer o/s).
Also how you have Montage connected to your sound system.

Also mention what instructions you are following. If you are making it up yourself, which is okay, but please let us know exactly what it is you ultimately want to accomplish.

Crashes and freezing can be hardware related or software related, but more often than not it is caused by a faulty configuration... What commonly called "pilot error". We cannot determine which from your description.

Let us know.