Error Code 0xC1900101.

Run SetupDiag and inspect the rollback logs before retrying, because 0xC1900101 is a generic rollback code—usually involving an incompatible driver—and does not identify the specific component by itself.^1^

1. Collect the actual failure details

A direct Windows Server 2016 → Windows Server 2025 in-place upgrade is supported with installation media on a nonclustered server. Windows Update does not provide this direct path from Server 2016.^2^

1. Sign in after the rollback and open:
   • C:\Windows\Logs\SetupDiag\SetupDiagResults.xml
   • Registry Editor → HKEY_LOCAL_MACHINE\SYSTEM\Setup\SetupDiag\Results
   Windows Setup normally runs SetupDiag automatically after a failure.^3^
2. If no useful result exists, download the latest SetupDiag.exe, save it as C:\SetupDiag\SetupDiag.exe, and run this from an elevated Command Prompt:

      mkdir C:\SetupDiag 2>nul
      cd /d C:\SetupDiag
      SetupDiag.exe /Output:C:\SetupDiag\Results.log /Verbose
      notepad C:\SetupDiag\Results.log
   

   SetupDiag requires .NET Framework 4.7.2 or later. If needed, check the installed version:

      reg.exe query "HKLM\SOFTWARE\Microsoft\Net Framework Setup\NDP\v4" /s
   

3. Record the following from the result:
   • Complete result and extend code, such as 0xC1900101-0x20017
   • Matching Profile Found or matched rule
   • Named driver, service, device, or application
   • Failure phase and operation
   If SetupDiag lists several failures, the last failure is typically the fatal one.^3^

2. Inspect the rollback logs

Use an elevated Command Prompt or enable File Explorer → View → Show → Hidden items and unhide protected operating-system files. Review:

• C:\$WINDOWS.~BT\Sources\Rollback\setupact.log
• C:\$WINDOWS.~BT\Sources\Rollback\setuperr.log
• C:\$WINDOWS.~BT\Sources\Rollback\setupapi\setupapi.dev.log
• C:\$WINDOWS.~BT\Sources\Rollback\setupmem.dmp
• C:\$WINDOWS.~BT\Sources\Rollback\*.evtx
• C:\$WINDOWS.~BT\Sources\Panther\setupact.log
• C:\$WINDOWS.~BT\Sources\Panther\setuperr.log

For 0xC1900101, the rollback setupact.log and event logs are primary evidence; setupapi.dev.log is particularly useful for device-install failures such as extend code 0x30018.^4^

Search upward from the last occurrence of the error code and correlate entries by timestamp. Also search for:

Shell application requested abort
Abandoning apply due to error for object

3. Remediate only the identified component

Depending on the result:

• Update or uninstall the named storage, RAID/HBA, NIC, chipset, or other device driver.
• If SetupDiag names disk encryption, antivirus, EDR, backup, or another filter driver, use that vendor’s supported removal or upgrade procedure.
• Update BIOS/firmware only through the hardware or VM-platform vendor.
• If the extend code is 0x20017, concentrate on boot/storage drivers, disk-encryption software, and possible hardware failure.
• If it is 0x30018, investigate the device named in setupapi.dev.log and disconnect nonessential peripherals.^1^

Before retrying, create and restore-test a full backup. Then mount matching Server 2025 installation media inside Server 2016, run setup.exe, and select Keep files, settings, and apps.^5^

Conditional fallbacks

• If SetupDiag identifies no component: perform a clean boot, disconnect nonessential peripherals, remove unused devices/drivers, and retry with a minimal driver and startup-service set.^1^
• If NIC Teaming is enabled: disable it before the upgrade and re-enable it afterward.^2^
• If this is a domain controller: do not continue with an in-place upgrade; install Server 2025 cleanly, promote the new DC, and demote the old DC.^5^
• If this is an Azure VM: first run the Azure VM OS Upgrade Assessment Tool and follow the Azure-specific procedure.^6^ If that procedure requires temporarily disabling security software or firewalls, this increases exposure—use a tightly controlled maintenance window with network isolation or equivalent protections, then immediately re-enable and verify every security control after the attempt.

Provide the complete result-plus-extend code and the SetupDiag matched rule to narrow remediation to the failing phase.

References

1. Windows 10 upgrade resolution procedures - Windows Client
2. Plan Your Windows Server Upgrade Path | Microsoft Learn
3. SetupDiag
4. Windows upgrade log files
5. Upgrade Windows Server in Place | Microsoft Learn
6. In-place upgrade for VMs running Windows Server in Azure