FBSOpenApplicationErrorDomain code =4 error
This worked for me:
iOS Simulator -> Reset Contents and Settings... -> Reset
referenced from Qiita: Unable to run app in Simulator エラーの対応方法.
Just closing the iOS Simulator worked for me.
There is not always the need to reset the iOS Simulator. I did not even had to close Xcode.
This happened to me once when I added some assets as symbolic links (through ln -sf). Even installing to devices was failing.
After I removed the links and made a hard copy, it worked and error was gone.