Xcode crashes whenever I try and Refactor

I 开发者_如何学Cget the following internal error message whenever I try and Refactor:

File:    /SourceCache/DevToolsIDE/DevToolsIDE-1708/pbxinterface/Snapshots/XCDirectorySnapshotSyncOperation.m
Line:    137
Object:    <XCDirectorySnapshotSyncOperation:0x201d51560>
Method:    _setErrorMessage:



Assertion failed: nil == _errorMessage

I have tried everything. I re-installed a new version of Xcode, I have tried re-installing the older version of Xcode nothing works?

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Try deleting the cache file referenced in the error and trying again.
The cache file could have become corrupt and causing the crash.
Also report this to Apple at http://bugreport.apple.com

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This was as simple as setting my target back to 5.1 (I was trying for 3 for max backwards compatibility) ... I assume I can set it back to target 3 before deployment , but leaving it a 5.1 whilst refactoring definately helped me