ios - 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.

No need to quit the simulator or reset all content every time .

Just close the app on which you are working if running on background .

it works for me .

As mentioned in the Xcode release notes, this error (along with a couple others) results from a timing bug. The workaround is to just retry.

See https://developer.apple.com/library/prerelease/mac/releasenotes/DeveloperTools/RN-Xcode/Chapters/xc6_release_notes.html#//apple_ref/doc/uid/TP40001051-CH4-SW1

Testing on iOS simulator may produce an error indicating that the application could not be installed or launched. Re-run testing or start another integration.

Also see:

https://devforums.apple.com/thread/248879?tstart=0