Key Commands must all have a Title, Key and Selector
Open your storyboard file as source code (right click -> open as -> source code). There should be a line, <keyCommands> <keyCommand/> </keyCommands>. Removing this should solve your problem.
This line can be caused by accidentally clicking the + button in the key commands section of the view controller's attributes inspector, although it may be caused by other factors. The extra line can cause weird things to happen in XCode, such as errors and crashes.
To do this with the xcode interface builder:
Select your view controller
Select attributes inspector
Find "Key Commands" list at the bottom
Select the keys within the list, such as: "Enter action below"
Hit the minus button
This should fix the problem.