Applescript: get path

[Jonathan Lewis]

An Applescript I'm writing needs to know the path to the currently open 
OO file.

OO's script dictionary shows three properties for the document class: 
path, modified, and name.

"Get name of document 1" returns the document's title as expected.

"Get modified of document  1" returns true or false as expected.

But "Get path of document 1" returns the error message 
"NSCannotCreateScriptCommandError".

What am I doing wrong? Any help much appreciated.

Mac OS 10.2.4
OmniOutliner 2.2(v55)

Jonathan Lewis