Error 3400 is usually associated with a problem in a drawing file, sometimes file corruption. There are many suggestions on troubleshooting possibly corrupt drawings in this KB article :http://support.microsoft.com/kb/826418 /
How to troubleshoot damaged drawings in Visio. You might want to work your way through these to isolate where the problem lies.
In the past, for instance, I've seen a lot of success recovering a problem file using the method to save the drawing as an XML drawing, when drawings can be opened but exhibit problems while in the editor.
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