Hi, very happy with Sonar Platinum. But one weird thing: when I put the cursor halfway the track (or any other place but the start/top of the track) to play from there, Sonar immediately aborts. Any ideas what causes this and how to solve that?

It would help if you told us a little more about your system and project.
 
What is your hardware (see my sig for example)?
 
What is in your project?  Midi?  Audio?  How many tracks?  What are your audio interface or driver settings?

try opening in safe mode. It might be a plug in causing the abort mission.
Im with Dave though, more info is needed. the more the better.

Thanks Dave and Chuck! This is my set up:
 
Intel® Core™ i7-6700 processor
16 GB DDR4 werkgeheugen480 GB SSD + 2 TB harde schijfNVIDIA® GeForce® GTX 750 Ti - 2 GBWindows 10 HomeAvid Mbox 2Sonar platinum
 
The abort happens in a project with 14 midi tracks, no audio. 

I am guessing it might have something to do with the Midi chase functionality.  Is this the only project that you have a problem with or is it every project?  It might be related to a specific synth, so opening in safe mode with the synths disabled might help diagnose it.  Of course, you won't get any sound if you have all the synths disabled, but the transport should start from the middle of the project.  You can toggle synths on and off to see which one crashes the project.