Messages Crashes on Mac Upon Startup Opened messages and the crash reporter immediately opened stating that the program crashed.  In the reporter it stated:


  Sandbox Creation Failed: You do not have permission to save the file "Application Support" to the folder "Library".


After some research the only possible solution I found involved creating a temporary account to see if its the system or user library and possibly having to delete your current account and creating a new, slightly different account and move your files to that new account.

My question was, is there an easier way to fix this without having to go through so much trouble?

(Hint: There is, or at least it worked for me.  Read on to the answer.)
Usually I activate the Guest account and use that to test issues like you're describing.

If you try with the Guest account and you're successful, it is an indicator that you've got permission problems with your files.

Unfortunately, Apple's Disk Utility doesn't fix users' files. I've generally found it is quickest to go into the terminal.app and look for permissions that seem out of the ordinary. For example, Application Support folder on my MBP is rwx------

You can view yours by opening Terminal, using cd Library to get into the right folder, then ls -lh to view the folders including Application Support.

If those permissions are different, we can show you how to change them.