This same issue is in InDesign CS5 running on Mac OS 10.6.8 and CS4 running Mac OS 10.6.8
From message id, 3794153, it appears this is an API error from Adobe.
You're passing it a string. Shouldn't you be actually passing it the preset itself?
You are on the right path. Actually, I found the answer in the ExportPDFWithPreset.applescript that was on the Adobe site with the manual. The correct method is to assign both the path and the preset to variables and then your code becomes
export format PDF type to myPath using mySettings.
The text in the manual is wrong, and has been for 3 versions. Shame on Adobe for lack of proof reading.