Here is an interesting error message when launching AutoCAD LT 2013 for Mac:
AutoCAD LT Alert The directory may be locked by another process or have been set to Read Only
In this case, we tried to fix permissions of Mac OS X on the computer by using Disk Utility but that didn't work.
To solve the problem, we needed to add Read & Write permissions to the /Users/users folder to get AutoCAD LT to work.
1. Highlight the /Users/user folder (or name of the user account that is having the problem). In this case, the user account was called: user.
2. Right Mouse click on the folder and select > Get Info.
3. Change the permissions to Read & Write for all user types.
Thanks to Stephanie E for confirming that this solution worked.