NOTE: the following refers to DP 5.1 on a Mac with OS 10.4.11… If you have a different version of OS X or if you’re running an older version of DP, things might be a little different
After cloning my drive with Carbon Copy Cloner and migrating to the clone, I found that Digital Performer wasn’t able to save files! Error Says:
An Error occurred while writing to the disk. The file [name] was not saved. This file was created in a later version of Digital Performer and cannot be opened in this version. Try to save your file on another disk or folder, or with a different name.
Oh no!

A little digging found me these Instructions from MOTU but they are slightly incorrect, at least they were for me.
The fix is to delete an invisible file called Auth-DigitalPerformer 5.0 from your Hard Drive’s root directory.
If you’re not comfortable doing things in the Terminal, File Buddy is a great app for this sort of thing. It’s like a souped-up Finder allows you to work with invisible files and do all kinds of other advanced things with the stuff on your Mac. It’s a very useful program but it does cost like $40 bucks.
A free Applications that will get the job done just as well is called Visibility and it’s made by a company called Zevrix Solutions. Download it, install it, launch it, click on Show Invisible Files, the Finder will relaunch, then you will see the file called Auth-DigitalPerformer 5.0 in your Root directory. Trash it and DP should be happy again. Afterward you can use Visibility to put the Finder back to normal.
Do be really careful not to move or delete any of the other invisible files. They’re hidden from you for a reason.
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The good news was that I found only you when it came to this problem. The bad news was that the procedure, though it went as described, did not work for me.
Agreed, you did say that the Leopard experience may be different, so maybe that’s it. I don’t know.
Since the search engine in MOTU’s tech support doesn’t work, you can turn grey before anything comes up there. I can’t even guess how you got that article from them.
In 10.5, incidentally, you can find invisible files through the “spotlight” search.
Anyway, I still have the same problem.