Thank you for your post.
It's a bit difficult trying to determine the cause when I can't see the file. However, the following may help...
If you created an envelope layout, did you include any fields on the layout? If so, pull down the View menu and select Preview Mode. This will show you how the envelope will print. Skip forward page to page to see the records. If they are all blank, then the field(s) you are using is probably blank, too.
Since you are in FileMaker Pro 9, go into Layout Mode (View menu), and on the left side, click on the Field tool and drag it onto the layout. Let go, specify a field, and go into Preview again. See if the information now displays.
If this works, then you may want to create another envelope layout with the appropriate fields again.
Let me know if you still run into difficulty.