I have the same problem with this printer (Photosmart 7520) . I have tried everything. I even set as 'default' the paper size 4 x 6" for the card tray, and the printer still tries to pull paper from (yes, the empty) large paper tray and sends me an error message. I have turned machines on and off. I have reloaded the driver.
This is clearly a larger problem that HP needs to resolve with this printer.
I have gotten it to print using the small paper tray, but God alone knows how it worked when it did. When trying the same an hour later, it refuses to work...and weeks later still doesn't work...then it will again for an hour or so.
Please will HP really try to fix this problem and share an answer with us. This printer is my second "give HP another chance" printer ... and I can promise there won't be a third if I have to give up on this printer, too.