Hi,
i always send a cakewalk .bun file from sonar platinum to a friend which has music creator 6. He always could open it.
In 2017.1 sonar he cannot open it. Error message: it's incompatible ....
What can i do? Any tips?
 

Have you opened the bundle in question in your own machine just to make sure it's not corrupt?
Bundle files can be rather sensitive. It may be that the second time you save it, it's ok.
I have no experience of the newer/older versions so I'm speaking very generally.

Yes, on my machine the bundle opens correctly. Maybe the new SPLAT 2017.1 bundle file is really not compatible with music creator 6?

AFAIK the bundle format has not changed in some time. The only features I know of that prevent a project from opening in older Cakewalk DAWs are patch points and aux tracks. Other new features cause warning messages but patch points and aux tracks cause open failures in Cakewalk DAWs that do not support them.

I have had some issues in the past opening old bundle files. I had saved them to a CD and checked them at the time. They checked good. Several years later, I went to open them on a version of MC and some opened, and some didn't. they gave me the "file corrupted" pop up.  
 
So I guess it is possible.   You might have to send waves.