You can resolve this problem one of two ways:
Remove the umlaut character from the QPS User name and then restart QPS Server.
Update to QPS version 7.4.
While umlauts are supported within the text stream of a QuarkXPress or QuarkCopyDesk 7.31, they are not supported in file naming or in user names in QPS 7.31. If the QPS User Name contains any umlauted characters when the user logs into the QPS Server, QuarkXPress and QuarkCopyDesk will crash. This problem is fixed in QPS 7.4.