A full support to CUPS 1.4 has been added since NX version 3.4.0. Please consult also the following articles: 

- How to print with NoMachine 4 and CUPS 1.4
https://www.nomachine.com/AR05K00674

- How printers and share works with NX 3.5.0:
https://www.nomachine.com/AR08D00413

In case of a less recent version of NX Server 3.x ,  adding a printer within the session could fail with recent versions of CUPS 1.4. The reason of this possible failure is described below.

To add a printer to the CUPS system, the  lpadmin command line tool has to be executed by a user who belongs to the CUPS's System Group, which can be for example 'lpadmin' on Ubuntu or 'sys' on Fedora distribution.

In a similar way, in order to let a user mount their client side printers in the NX session, NX node needs to change on the fly the group of this user to the CUPS System Group with help of SGID and to execute the lpadmin command line tool. 

However, recent versions of CUPS 1.4 don't use local certificates for authorization of command line tools like lpadmin executed locally, which is at the base of the mechanism used by NX to retrieve and set the proper CUPS System Group.

As a possible workaround, on those systems where CUPS 1.4 is installed (e.g. Fedora 11 and Ubuntu 9.10) to let NX users print to their local printers, the administrator has to add all of these users to the CUPS  System Group.