Firstly, please try the troubleshooting steps in this article if you haven't already.
If these do not help, please try reinstalling the VNC Printer Driver on the VNC Server computer. To do so, please choose one of the 2 methods below. After completing either method, disconnect and reconnect your VNC Viewer and try printing again.
Reinstalling Printer Driver
Command line method
Open an elevated Command Prompt by searching for Command Prompt in the start menu, then right clicking the Command Prompt result and clicking Run as Administrator. Run the below commands:
cd "C:\Program Files\RealVNC\VNC Server\Printer Driver"
Firstly, with no VNC Viewers connected to the VNC Server, remove any printers listed on the VNC Server that include "via VNC" in the name.
Next, you need to remove the VNC Print Driver from the VNC Server computer. To do this, you need to use the Print Management utility in Windows. You can access it by searching for Print Management in the Start Menu.
In the Print Management utility, locate the VNC drivers by clicking the Custom Filters section, and then All Drivers. Look for VNC Printer (UD) and VNC Printer (PS) (see below screenshot).
Right click each one and then select "Remove driver package".
After both VNC drivers have been removed, run a repair install of VNC Server. To repair VNC Server you need to go into Control Panel, then Add/Remove/Uninstall programs. Find VNC Server on the list, and then click Repair above the list.
We recommend running the repair install this with someone on-site with the VNC Server computer should something go wrong during the repair operation preventing you from accessing VNC Server remotely.