If the file wasn't listed in the Open Recent submenu, there's always the possibility that it was cleared recently. We can outline steps for manually navigating to an iCloud document, if you ever face a similar situation again.
Now, we'd be curious to learn about how that PLIST file ended up there as well. Are you certain it was created by CheckBook Pro? Only pre-2.5 versions save data to that format and it's been roughly a year and half since 2.5 was released, so you shouldn't still have 2.3.2 or earlier installed. All applications use PLISTs to store preference information, though. If you kept the PLIST around, feel free to send it to us at
support@splasm.com as we'd be happy to look at it to try and determine what application created it.