hi, I created a new project, the BP car game, I opened the anim BP and when I tried closing the viewport showing the car I get 2 messages (mostly about slate) and after closing the messages rocket freezes completely.
I also tested with the BP side scroller and got the same thing.
If you could tell the error message or post a screenshot then it will help Epic devs to solve the issue. 
yeah I was going to add the messages but it was late.
anyway here is a text file I copied both messages into.
link text
Hi Michael,
Thank you for the report. I have confirmed that this issue occurs in Rocket upon closing the Viewport in any Animation Blueprint.
I have also tested on our current internal build and the issue is no longer occurring. It appears to have been fixed since the Beta 5 release and is not expected to be an issue in future Rocket releases.
Cheers!
ok, thanks