This can happen when DP files are emailed as attachments. It's a good idea to use Finder>File>Create Archive to create a .zip file and email the archived file.

Digital Performer project files have a Mac file type of "PERF" and a creator of "MOUP". If you have DP files which have become damaged or corrupt in some way and they can no longer be opened by Digital Performer because they are grayed out in the File > Open dialog, the file type and creator may need to be reset to their proper values. This can be accomplished with third-party file utilities like FileBuddy, FileType, and Quick Change, or using the SetFile command in Terminal (OS X Developer Tools must be installed).
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