What paper size is specified when you print or preview your layout? any chance that a custom paper size intended for the Dymo is still specified?
If you are using a script to print, check this first with a manual print from the File menu or just enter preview mode to keep any script issues from being a factor.
Is this a hosted file? (hosted from FileMaker server or FileMaker Pro on another computer)
If so, take one of these files down off the server and open it directly with Filemaker from the same computer where you've copied the file. Now try changing settings.
Normally, I'd also suggest entering layout mode and checking the print settings inside layout setup, but it seems unlikely that all layouts from several files would have the same settings here.
You might also create a brand new, small test file with just a few fields and one layout to see if it exhibits the same behavior or not.