Typing "defaults write com.apple.dt.Xcode DVTDisableMainThreadChecker 1" in terminal worked for me. And then opening xcode, asked to install additional components. Thanks
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
this particular terminal note fixed my original issue. And as noted above, was prompted to install additional components. When agreeing, I get a message box which says "An unknown error occurred. See the install log for more details" when i click try again it attempts for split second and then this message comes right back up. Anyone know a work around here?
aaaand the cause was xcode was still updating...
@negiruh Thank you! That did the trick!
I had the same issue where I have multiple versions of Xcode to practice along with different Xcode books. Xcode 10.0, 11.3, and 12 all worked fine after downloading. This 10.2.1 version kept giving me the crash error and I needed this version to run some code from a different book. Tried replacing the libMainThreadChecker.dylib from 10.0 and 11.3 and it didn't work for me. The file from Xcode 12 worked so now Xcode 10.2.1 works for me. Hopefully this helps anyone with similar issue.
I am very worry personally in running any terminal commands in case fixing the 10.2.1 would break my other Xcode versions.
Would suggest to make a backup with Time Machine or Super Duper before making changes like this.