Printer Drivers

Hi All,
We've just completed a desktop application and sent to clients. During our testing there was no problem with printing (we tested in our HP laserjet printers). However, clients logged their complaints since they could not printing on their printers (either Epson or Lexmark or any printers with their manufactures' printer drivers but not from window's printer drivers). I searched for similar problems in Sun's forums but returned with all questions asked but no solution.
Does anyone know this is a problem or bug in printing API? Why does printing work with a printer but not for other?
Thanks in advance for any help.
Regards