Fixing broken Messages on OS X Mavericks I managed to break my Messages install trying to get it to work on my MacBook Air by deleting Library files that worked with it. Now when I try to open messages I get the error 


  An internal Messages error occurred.
  
  
    There was a problem with Messages. You need to quit and open Messages again.
  


Can I just copy Library files from another one of my computers running OS X? Or is this the sort of thing that I need to reinstall the OS for?
Yes, copying the files from another computer should be fine, providing both computers have the same version of Messages.

There is a certain amount of leniency with this though, depending on where the files are that you deleted. For example, files in your home folder are expected to be backward-compatible since if you've upgraded your OS then it must know how to update the files.

Also, once you've copied the files, make sure you set the permissions correctly…


If you've copied files to /Library, use Disk Utility to repair permissions.
If you've copied files to ~/Library, use the ACL tool on the Recovery HD.