I was doing some work in Quark the other day and started getting strange “unknown errors” on a document that prevented me from either modifying it in any way or even saving it. A few years ago I would have persevered with the document and tried to find the root cause of the problem. Now, I just put it down to Quark being Quark and realise its one of little problems that occurs from time to time. My advice is, don’t bother messing around with the corrupted file, simply create a new document, and group your layout. Then paste it into the new document and give it a different name, for me it fixes the problem every time.