1、
fatal error: file '/Applications/Xcode5-DP.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator7.0.sdk/System/Library/Frameworks/UIKit.framework/Headers/UIDynamicAnimator.h' has been modified since the precompiled header '/Users/sumomochuufuku/Library/Developer/Xcode/DerivedData/ModuleCache/2NEVAP7X943D2/UIKit.pcm' was built
note: after modifying system headers, please delete the module cache at '/Users/sumomochuufuku/Library/Developer/Xcode/DerivedData/ModuleCache/2NEVAP7X943D2'
1 error generated.
解决办法：前往 '/Users/sumomochuufuku/Library/Developer/Xcode/DerivedData/ModuleCache/2NEVAP7X943D2 这个文件夹，删除其文件夹中的内容，然后运行app，没问题了，注意不是删除 2NEVAP7X943D2 文件夹，而是其中的内容。然后再 clean下项目就可以了（product -> clean）
注意：
1)、 sumomochuufuku 是我的用户名，你要改成你自己的。
2)、NEVAP7X943D2 文件夹应该是对应应用的，所以会随着app的不同而改变，要理解并灵活使用。
2、
fatal error: file '/Applications/Xcode5-DP.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator7.0.sdk/System/Library/Frameworks/UIKit.framework/Headers/UIFont.h' has been modified since the precompiled header '/Users/lucky/Library/Developer/Xcode/DerivedData/ModuleCache/15I6PGVCGLZMV/UIKit.pcm' was built
note: after modifying system headers, please delete the module cache at '/Users/lucky/Library/Developer/Xcode/DerivedData/ModuleCache/15I6PGVCGLZMV'
1 error generated.
解决办法：同错误1
前往 /Users/lucky/Library/Developer/Xcode/DerivedData/ModuleCache/15I6PGVCGLZMV 这个文件夹，然后删除文件夹中的文件，然后clean下项目。
类似错误，需要清除缓存来解决的，以后不赘述了