Look familiar? This message resembles the one you saw on the previous page of this course. In this case, though, the warning tells you that the PST file can't be opened. The most likely cause is that someone else already has the file open and so has locked you out.
How can that happen? Although you'll get the best performance with PSTs when they're stored on your own computer, it is possible to open a PST that's stored on any other computer on your network — as long as you have appropriate permissions and as long as no one else has that PST file open. To avoid problems, remember that PST files are for use by one person at a time, on one computer at a time.