3.01b3 XML export error?

[Byron]

Hi All,
Apologies if this has been covered. I Have a 1.6 MB multi-canvas 
document which I have just attempted to export to a Visio XML, & got 
the error/alert:

"*** -[NSCFDictionary setObject:forKey:]: attempt to insert nil value"

Using Omnigraffle Pro 3.01 b3
A trial with a small one page drawing didn't generate an error.
Anyone have any knowledge/experience  of this as an issue?

Thanks,

Byron

Byron Stevens
Infonautics Software Solutions Inc.
User Experience and Information Design
User Centered Design
User Interface Design
905.836.1753