[einarnn]

My mistake. I tried adding in the alias while debugging and I get the same result with or without the alias, namely:

tell application "AppleScript Editor"
	choose file with prompt "Select an Omnigraffle file"
		--> alias "Macintosh HD:Users:einarnn:Documents:Work:eEdge:acl-stuff.graffle"
end tell
tell application "OmniGraffle Professional 5"
	open alias "Macintosh HD:Users:einarnn:Documents:Work:eEdge:acl-stuff.graffle"
Result:
error "OmniGraffle Professional 5 got an error: AppleEvent timed out." number -1712

And I can also try to open the file directly by name, which gives me this result:

tell application "OmniGraffle Professional 5"
	open "Macintosh HD:Users:einarnn:Documents:Work:eEdge:acl-stuff.graffle"
Result:
error "OmniGraffle Professional 5 got an error: AppleEvent timed out." number -1712

Note that in each case, the file opens successfully. The problem is just that my script is hosed as the script never gets the result.