Check with MS RDC client first.
Check with our demo gateway
Make sure there is no "Printer redirection: false" in the log file which means this feature is disabled (on the client side or server side) or your license file expired.
Printing service is working in RDP host (try print something)
Printer redirection is enabled in RDP host.
You domain controller is not Windows 2003 or before.
Spark View use "MS Publisher Imagesetter" as the driver of "Remote Printer from Client", please check if you can see this printer driver when you try to add a printer (Under "Generric" manufacturer). If not, you can let Spark View use other GhostScript Printer Driver in gateway.conf.
Same printer driver may have different name on Windows 2003 or before. You can map the drive names in Windows 2003.
Try disalbe Easy Print.