You may have a bad connection in your xib.

I've had this error many times. While TechZen's answer is absolutely right in this case, another common cause is when you change the name of a IBOutlet property in your .h/.m which you've already connected up to File's Owner in the nib.

From your nib:

1. Select the object in IB and go to the 'Connections Inspector'.

2. Under 'Referencing Outlets' make sure that your object isn't still connected to the old property name... if it is, click the small 'x' to delete the reference and build again.

   

Another common cause if you are using Storyboard, your UIButton might have more then one assignings (Solution is almost the same as for nib):

1. Open your storyboard and right click the UIButton

2. You will see that there is more than one assign/ref to this button. Remove one of the "Main..." greyed windows with the small "x":

   

Here's what I'm doing:

1) In my framework CMakeLists.txt file, I have the following:

IF (APPLE)
       SET_TARGET_PROPERTIES( MyFramework PROPERTIES FRAMEWORK true)
       SET_TARGET_PROPERTIES( MyFramework PROPERTIES
           XCODE_ATTRIBUTE_INSTALL_PATH @executable_path/../Frameworks/  )
ENDIF (APPLE)

The second "set_target_properties" line configures the framework to always be looked for in the application bundle in the Frameworks sub-folder.

2) In my top-level CMakeLists.txt file, I add setup a unified binary output directory:

SET (CMAKE_LIBRARY_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/Bin)
SET (CMAKE_RUNTIME_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/Bin )
SET (CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${PROJECT_BINARY_DIR}/Bin )

3) Then, in my applications' CMakeLists.txt file, I have the following:

IF (APPLE)
       ADD_CUSTOM_COMMAND(
               TARGET MyApp
               POST_BUILD
               COMMAND ${PYTHON_EXECUTABLE}
               ARGS ${CMAKE_HOME_DIRECTORY}/CopyFramework.py
               --binary ${PROJECT_BINARY_DIR}/Bin
               --framework MyFramework.framework
               --app MyApp.app

    )
ENDIF (APPLE)

This calls out to my python script, which does the work of assembling the src and dest paths, and actually copying the Framework.

The final trick is that since this is a Mac only thing, I can rely on an Xcode environment variable within the Python script:

           config= os.environ["CONFIGURATION"]

This allows me to assemble the complete path to the actual binary locations of the framework and the app.

The one thing I wish was that there was a CMake variable that would expand to the current Config within the context of the ADD_CUSTOM_COMMAND... It'd be nice to not have to resort to using the Xcode environment variable.