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?

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

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