It is a disapointing fact that some HP Deskjet Printers do not have the correct drivers to work via citrix.
I have contacted HP about this and they openly admit that some of there drivers are incompatible with Citrix (Terminal Server).
I have had direct experience with the HP 800 series printers and can say without doubt that they are incompatible. Reading other posts and other responses it is safe to say that most HP Deskjet printers have problems printing via Citrix.
My suggestion is to stay away from HP Deskjet printers when printing from Citrix. Especially when they are "critical" printers. But, if you have already purchased an HP Deskjet printer that will not print - you can try installing different HP drivers. Yes, it is a guessing game - but it is the only option you have if you can't take the printer back for some reason.
I hope this helps everyone and if anyone else finds any other incompatibilities - PLEASE LET US KNOW!!!