IOS project showing error "An internal error occurred. Editing functionality may be limited" on xcode 7.1

I had this issue and clearing derived data folder fixed the issue for me

Preferences > Locations > Derived Data > click the arrow to open in Finder > trash it.

Try this, it's work for me,

Updated NOTE: Mostly this error occurred when you have open 2 different version of Xcode at same time.

Solution: Please close both Xcode and clear derived data.now again try, use one Xcode at a time.

OR

Follow below mention steps ,

1) Trash derived data by two ways either by command or Preferences.

rm -rf ~/Library/Developer/Xcode/DerivedData/

OR

Xcode---> Preferences--->Location--->Derived Data

2) In Xcode menu go to product clear the project.

3) Disconnect connected device and restart Xcode and system .

follow above steps error will remove.

Hope it's helpful for some one.

Fixed the problem in my program, hope this can help someone!

So, this is the process of my fix:

1. Could not figure out why I was getting this issue, when everything had been working fine.

2. I tried the following:
   Cleaning project
   Deleting DerivedData
   Creating new, identical View Controllers to see if the issue was just in those particular views. (the same issue occurred)
   Deleting and Reinstalling Xcode
   Restarting my Computer.
   Asking on StackOverflow.
   (Finally) Submitting a TSI, which got redirected to Apple Bug Reporter.

3. I made a new swift file for the View Controller that was having the issue, and it compiled, showing that is was not an issue with the View Controller itself.

4. I started getting an error: "Command failed due to signal: Segmentation fault: 11" (on the file associated with the View that did not work), which is really ambiguous. This error looks as if it would be an error occurring in a segue (jumping from one View Controller to another) but the code itself would not compile. After digging into the error, I realized the code stopped compiling at that swift file.

5. So, I copy-pasted the code from the swift file (the one causing problems) into the Notes application and I deleted the swift file from the Application.

6. Little by little, I started taking code from the file that did not work (in Notes) and putting it into the file that did work until the error came up:
   

   Command failed due to signal: Segmentation fault: 11

7. I started commenting out snippets of the code to isolate the error.

8. After finding the error line, I realized it was just an error that caused all of these issues. A simple fix that the debugger did not recognize as a routine error. So, I fixed it and it works!

And for those of you less inclined to read

Summary of what your problem may be:

• Compile-time error in your code that is not recognized by the Xcode debugger!