All you need is in the NX install. - NO other software needed.
This error is difficult to answer with only "unknown system error" as clue.
You need either upload a syslog here for us to look in, or call the GTAC for assistance. ( They will also ask for a syslog.)
If you don't know what a syslog is: In NX, Help - NX logfile, save this text as a plain textfile.
Note that the logfile does contain some information about you/your company.
If you like to upload it here you should strip away the "first pages" of the syslog.
Also, when submitting syslogs, it is easier for the support if you create a new logfile by 1 start NX, 2 load something, 3 try the export PDF, 4 help - NX logfile, and not save the logfile after a full days work. It does contain information about all(!) the clicks you have done from start of the session.
Regards,
Tomas