GridTemplate is a Macintosh file
This message occurs if you try to use a QuarkXPress file that was last saved on a Macintosh as part of a DiaryGridLine.
The solution is to use the Windows version of QuarkXPress to open that file and save it. It will thus be saved as a Windows file and the present message will disappear.
In the extremely unlikely event that this message is generated incorrectly, you can change its level from and error to a warning by checking the Version mismatch is only a warning option of the QuarkXPress page of the Q++ Preferences.
This is, however, not recommended.