问题:

After migrating from XCode 5.0 to XCode 6.0 the project fails to run with the following error.

An error was encountered while running (Domain = FBSOpenApplicationErrorDomain,
Code = 4)

Any suggestions?

回答1:

iOS Simulator -> Reset Contents and Settings

Worked for me!

iOS Simulator -> Reset Contents and Settings... -> Reset

referenced from: http://qiita.com/tajihiro/items/f6f50b56162c93d25c90

回答2:

I had this error too. My solution was product->clean

回答3:

As described in my answer to the queation that this is a duplicate of, this error is one manifestation of an install/launch race condition bug. The suggestions you find on this forum suggesting that you should "Erase Contents & Settings" or "Clean" from within Xcode are not correct.

You simply have to try again and hope you don't loose the race on the next launch. Alternatively, you can just "finger launch" it from within the booted simulator.