Xcode6:Embedded binary is not signed with the same certificate as the parent app
Solution 1:
I had to select my app under 'Targets', then go to the 'Capabilities' tab and click 'Fix Issues' under the 'App Groups' section
Solution 2:
I had discrepancies under Code Signing. My Extension and Main app had different certificates selected. Once I set both to use distribution it worked fine.
Solution 3:
In the case of using WatchKit, make sure that your Watch App has the correct "Team" selected in the Watch App Target settings (under General > Signing > Team). I had set the phone app's team, but not the watch app's team.