Hello PeterS,
From your description, the redirected printer is appearing correctly in the session with a TS port assigned, which means the redirection handshake between the RDP client and the RDS host is working. The failure when printing a test page indicates that the driver handling on the server side is not aligned with the redirected device. Since you have disabled Easy Print and fallback driver behavior, the server is attempting to use the native OKI driver. If that driver is not installed or not fully compatible with RDS redirection, the print job will fail.
The first diagnostic step is to re‑enable Easy Print temporarily. Set Use Remote Desktop Easy Print printer driver first to Enabled in Group Policy (Computer Configuration > Administrative Templates > Windows Components > Remote Desktop Services > Remote Desktop Session Host > Printer Redirection). Easy Print uses the XPS driver built into Windows and bypasses the need for the native printer driver on the server. If printing works with Easy Print enabled, the issue is driver compatibility.
If you require native driver support, you must install the exact OKI C310 driver on the RDS host. Confirm that the driver is present under Print Management > Drivers on the server. If it is missing or mismatched, add it manually. Also check the registry key HKLM\SYSTEM\CurrentControlSet\Control\Print\Printers to ensure the redirected printer is mapped correctly.
To diagnose further, enable logging for printer redirection. In Event Viewer, look under Applications and Services Logs > Microsoft > Windows > TerminalServices-Printers. Errors here will show whether the print job is failing due to driver mismatch, spooler issues, or redirection policy.
In short, the problem is that with Easy Print disabled, the server requires a matching driver for the redirected printer. Either enable Easy Print to bypass driver dependency or install the correct OKI driver on the RDS host. Event Viewer logs will confirm the exact failure point.
I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!
Domic Vo.