Interface Builder - Failed to load designables from path (null)

I had the same issue. I use cocoapods and there is a pod which uses designables. So the trick was to add 'use_frameworks!' to the Podfile. do a 'pod update' reopen the xcode project and the error message shouldn't show up.

Edit**

Open Xcode (but do not open your project) and click on Window (second from the right)

Click Organizer and make sure you're on Projects, then delete all derived data. Close out Xcode and then reopen your project and let Xcode re-index your files and see if that clears up the issue

I'm running Xcode 7.3, and got the error to magically disappear by following these steps that, in the end, left my project in the exact state that it was prior to following these steps (i.e. a net zero change to anything):

1. Add 'use_frameworks!' (without the apostrophes, of course) to yourpodfile
2. Open up a terminal window
3. cd to your project's root dir
4. Run 'pod install' from the command line
5. Remove the 'use_frameworks!' from your podfile
6. Run 'pod install' again
7. Try building again and see if that fixes theerror; it did for me

Looks like one of those occasional Xcode snags that we've all seen before, especially when you're in a hurry to get something else done.