Please ensure that the Amyuni PDF Converter is assigned to the NUL: port on all x64 PC's. It can be found under the Printer properties under the Ports tab.
Attaching the PDF Converter to a port called NUL: is actually the solution provided by Microsoft to resolve a situation that will occur if you create a custom printer port on a 64bit version of windows.
On some 64bit PCs the PDF Converter may become unresponsive or "hang" while printing when the printer is using a custom print port name or LPT1. This "hanging" is caused because the print spooler will create a temporary file in the windows\system32 directory when printing. When a non admin user tries to print, the print spooler will try to access this temporary file in the windows\system32 directory. However non-admin users do not have access to the windows\system32 directory and this causes the "hanging" when printing.
We opened a support issue with Microsoft and they suggested a solution that involves creating a special printer port called "NUL:". When a printer is attached to this port, the printing does not use the printer spooler, thus no temp file is created and resolves the "hanging" issue.
When our installer (version 4.0) is executed on a 64bit PC, the installer checks the system for a port called “NUL:” (upper case). If this port is not on the PC, the installer creates the port and attaches the printer to this port. In the case where the port is already on the system, the installer simply attaches the printer to the port. If the installer is unable to create a NUL: it attaches the printer to the LPT1.
The procedure of creating a printer port called “NUL:” (upper case) was sent to us by Microsoft as a way of installing our driver on 64bit OSs. However when Microsoft’s OneNote application is installed on a PC, it installs a printer driver and creates a printer port called “nul:”(lowercase). Microsoft tells us to create a port called NUL: and they create one called nul:
What is happening is our installer is case sensitive and is trying to create a port called “NUL: ” (upper case - Microsoft recommendation). The creation of the port is failing because the port is already on the system (“nul:” - lowercase ) and our installer is attaching the printer to LPT1.
You can test this by trying to create a “NUL: ” (upper case) on a PC that already has a “nul:” (lower case). Windows will complain that the port already exists.
In order to resolve this issue you simply need to attached the PDF Converter to the “nul:” port. There are no problems with having multiple printers using the same port.
NOTE: In the current version v4.5 of the PDF Converter the installer is not case sensitive when checking for the port name.