Playback Error in Multitrack

Ok. I think I've found the problem but I don't know how to fix it. I'm working as said with a 5.1 project and I have a 5.1 surround sound device connected to my pc and in the system sound settings I've set the device configuration to 5.1, too. But in Audition only the left and right channel is found athough all is set to 5.1. Why?

Well, whatever's causing this, it will still come down to the same thing; something about your sound device is either upsetting Audition, or has made it invisible. Without having your machine in front of me, I cannot tell what is happening, I'm afraid. You may need to get somebody local to look at it.

I've set the ouput rate to 48000, same as the project is. The project also is a 5.1 Surround Sound project and in the system sound settings I also configurate my output speaker to 5.1. But again nothing has changed. I can't playback my project.

If you click on Setttings, it will take you to the page for the device itself. Something, somewhere in there isn't functioning correctly. There really isn't anything else that stops Audition's transport, so it has to be something in there. One thing that may make a difference is the input sampling rate, which isn't the same as the output rate. Not all internal devices are happy running like this. I'd suggest setting that to 48k as well. Also you could try taking the check out of  'use machine-specific device defaults' and see if that makes a difference.

And what exactly shell I change, cause this are my actual settings and the input and output are always my system standards.

This means that your sound device isn't correctly connected to Audition - this is the only thing that stops the transport. You need to go into Edit>Preferences>Audio Hardware to correct this.