The reason for receiving this message is most likely because the location where you are trying to open from is not available and is most often related to a network drive and occurs because you IT team has locked the file for some reason.
Solution
Copy the file from the network drive to your desktop and try to open the file again.
If that fails an alternative it to recover the most recently saved file. AuditSoft makes periodic backups of your audit file. You can read more here: