What i understand from your problem is, you are trying to work on a QuarkXPress document by opening it over a network. Technically, it should work well. Please note that QuarkXPress is not guaranted to work on network. The workaround is copy the QuarkXPress document to your workstation and then open the file. After working on it save it on ur workstation then tranfer to the server.
When QuarkXPress opens a file over a network, the page you see on your sreen is only in the cache, hence at no time the entire document is present thus any network error can cause an error.