You must upgrade QuarkXPress to version X, preferably Y
This message occurs if you are using a minor version of QuarkXPress which has been determined to be too unstable to use.
For example, under QuarkXPress 7, the minimal stable minor version is 7.31. If you are currently using QuarkXPress 7.0, 7.1, 7.2 or 7.3, then the present message will appear.
You should look at the minimal minor versions of QuarkXPress required and go to the Quark website to download and install that minor version at least.