After installing Xcode 7 I can't build and run projects anymore as document fails to open

Question

EDIT: This question refers to teh pre-release version of Xcode 7, hence it may not be relevant if you are running the currently released version as some issues may have been

Answer 1

I ran into the same issue with xcode 7 beta 3.

I had my deployment target set to 8.3. Setting it to 9.0, cleaning the build, and restarting xcode worked for me.