It works, thanks You can fix this by replacing the 'libMainThreadChecker.dylib' file with the one in the working Xcode. Go to this path on both the Xcode's you have, beta and 10.3: /Xcode.app/Contents/Developer/usr/lib and copy the file from the Xcode that is working to the one that is crashing. Posted 8 months ago by yanincontreras