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…
