When you enable the Virtual Printing option during Horizon Agent installation, users can print from remote applications that they launch from Horizon Client inside remote desktops (nested sessions) to printers on their local client machine.
Beginning with Horizon 7 version 7.0.2, users can print from remote applications launched inside a nested session to printers connected to the remote desktop machine rather than to printers connected to their local client machine. To enable this feature, change the Thinprint session-in-session mode on the remote desktop machine by changing the value of SiSActive to 0 in HKEY_LOCAL_MACHINE\SOFTWARE\ThinPrint\TPClnRDP.
When SiSActive is set to 0 on the remote desktop machine, users can no longer print from remote applications launched inside nested sessions to printers connected to their local client machine. To reenable the default ThinPrint session-in-session mode, change the value of SiSActive to 1 in HKEY_LOCAL_MACHINE\SOFTWARE\ThinPrint\TPClnRDP on the remote desktop machine.
For information about enabling the Virtual Printing option during Horizon Agent installation, see Horizon Agent Custom Setup Options for an RDS Host.