Title: Server 2025 print server pushes 26100 core printer package to Server 2016 / Windows 10 clients - UNIDRVUI.DLL 0x7F, connection fails with 0x000003eb Hi all, We're seeing a printer connection issue after moving our print server to Windows Server 2

Question

Title: Server 2025 print server pushes 26100 core printer package to Server 2016 / Windows 10 clients - UNIDRVUI.DLL 0x7F, connection fails with 0x000003eb Hi all, We're seeing a printer connection issue after moving our print server to Windows Server 2

Maheswaran Shanmugavelu 40

Hi all, After moving our print server to Windows Server 2025 (build 26100.33438, September 2026 update), Server 2016 and Windows 10 clients can't connect to shared printers. Server 2019, 2022, 2025 and Windows 11 clients work fine against the same server. The connection gets to "Finishing the installation..." and fails with 0x000003eb. The client logs Event 808: "The print spooler failed to load a plug-in module C:\Windows\system32\spool\DRIVERS\x64\3\UNIDRVUI.DLL, error code 0x7F." Drivers are Type 3, Unidrv-based (Xerox GPD PCL6, Ricoh PCL6). On a fully patched Server 2016 client (14393.9512), UNIDRV.DLL had been replaced with the 26100.33438 version, and a 26100 ntprint core package had been added to the driver store from the print server. We removed the drivers and the 26100 package, restored the original 14393 UNIDRV.DLL, and pre-installed the printer driver locally. The spooler came up clean. But on reconnecting to the printer, the 26100 package was pulled down again and the failure returned, every time. This looks similar to the reports of Unidrv files breaking Type 3 printing after the September 2026 updates, but I couldn't find a Microsoft known issue for it. Is this expected behavior, and is there a fix or a supported way to stop the newer core package being sent to older clients? Has anyone seen a change with the October 2026 update? Thanks!

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Answer accepted by question author

James Gamble 170

Hola Maheswaran,

What you're seeing aligns with a documented Windows Server 2025 printing compatibility change, although your exact UNIDRVUI.DLL error isn't explicitly called out in the current known issues list.

Starting with the September 2025 Windows Server 2025 update, Microsoft changed parts of the Windows printing stack from the older MSVCRT runtime to the Universal C Runtime. Microsoft explicitly states that older Windows Print clients can intentionally fail when connecting to an updated Windows Server 2025 print server. Microsoft documents the change here.

The important part is beside the Print items. Microsoft says clients older than Windows 10 version 2004 / Windows Server version 2004 aren't compatible with this updated remote-printing path, and their supported workaround is either to upgrade the client or have those older clients use a pre-Windows Server 2025 print server.

That makes Server 2016 seem like a problem here. For the Windows 10 machines, I'd check their exact version/build before assuming they're affected for the same reason. If they're older than the supported level, that would fit Microsoft's documented behavior.

Your observation that the 26100 core package comes back after reconnecting also makes sense with how package-aware Type 3 drivers work. Unidrv is a Windows core print driver. During Point and Print, Windows can install the core driver package required by the printer driver, and Microsoft documents that the installer selects the newest applicable core driver package from the driver store.

So I wouldn't try to pin or manually restore the older UNIDRV files on the client. As you've already found, Point and Print just reverts the newer dependency, and manually mixing core print files from different Windows versions isn't a supported fix.

I also couldn't find a Microsoft-documented switch that tells a Server 2025 print server to keep serving an older Unidrv core package to legacy clients. Microsoft's documented compatibility guidance points the other direction: upgrade the clients, or keep a pre-Server 2025 print server available for older systems.

One thing I'd verify before calling the Server 2019 result definitive is whether that machine already had the printer/driver installed before the Server 2025 migration. Since Server 2019 is also older than build 19041, a fresh connection from a clean Server 2019 client would be a useful comparison.

Thanks,

James

Maheswaran Shanmugavelu 40 Reputation points

2026-10-13T17:07:42.1633333+00:00

Hi James, I really appreciate your time; this helps convey to the customer, per MS std.

1 additional answer

Your answer

Maheswaran Shanmugavelu 40 Reputation points

2026-10-13T17:07:42.1633333+00:00

Hi James, I really appreciate your time; this helps convey to the customer, per MS std.

Answer 1

Hello Maheswaran,

Thank you for posting your question on the Microsoft Windows Forum!

Thank you for the detailed investigation. Based on everything you've already tested, I would avoid repeating generic printer troubleshooting because you've already isolated the issue quite well.

A few findings stand out:

The issue only affects Windows Server 2016 and Windows 10 clients.
Server 2019/2022/2025 and Windows 11 clients can connect successfully.
The failure occurs when the print server pushes a newer 26100.x core print package.
The client logs show:

UNIDRVUI.DLL

error code 0x7F

Restoring the original 14393 Unidrv files temporarily resolves the issue until the printer connection pulls the 26100 package again.
Both Xerox and Ricoh Type 3 Unidrv-based drivers exhibit the same behavior.

This strongly suggests a compatibility issue between the newer Windows Server 2025 print core components and the older Windows 10 / Server 2016 printing stack, rather than a vendor-specific Xerox or Ricoh driver issue.

Step 1: Verify the Exact Package Being Downloaded

On an affected Server 2016 client, before and after connecting to the printer, collect:

Open CMD as administrator:

pnputil /enum-drivers > drivers.txt

and identify the package associated with:

ntprint.inf
UNIDRVUI.DLL

This helps confirm whether the newer core package is consistently replacing the inbox Server 2016 version.

Step 2: Check PrintService Operational Logs

Please review:

Event Viewer
→ Applications and Services Logs
→ Microsoft
→ Windows
→ PrintService
→ Operational

around the time of the failure.

In particular, look for:

Driver package staging
Package installation failures
Core driver replacement events

These events often reveal why the spooler is accepting the newer package and whether the failure occurs during staging or loading.

Step 3: Test with Point-and-Print Restrictions Disabled (Temporary Test)

If permitted in your environment, temporarily test using:

Computer Configuration
→ Administrative Templates
→ Printers
→ Point and Print Restrictions

to determine whether package acquisition behavior changes.

This is only for troubleshooting and not as a permanent recommendation.

Step 4: Compare October 2026 Client Behavior

You specifically asked whether October 2026 updates change the behavior.

I would recommend testing:

One fully patched Windows 10 system
One fully patched Server 2016 system

with all October 2026 updates installed and collecting fresh PrintService and System logs after reproducing the issue.

Additional Information Requested

From the affected client, what is the file version of:

C:\Windows\System32\spool\drivers\x64\3\UNIDRVUI.DLL

after the failed connection attempt?

My Assessment

Given that:

Multiple printer vendors are affected.
Older OS versions fail.
Newer OS versions succeed.
The issue consistently reappears after the 26100 core package is pulled from the Server 2025 print server.

I would currently suspect a print core compatibility regression involving the newer Unidrv package rather than a Xerox or Ricoh driver defect.

I hope this answer has brought you useful information. If so, please click on "Accept Answer" and consider upvoting it. Doing so helps other community members identify useful solutions to similar issues.