"'MSOLEDBSQL19' provider is not registered", but it is, and runs fine for weeks

Question

"'MSOLEDBSQL19' provider is not registered", but it is, and runs fine for weeks

David Weigel 0

We have a web application that runs with a connection string of

Provider=MSOLEDBSQL19;uid=:U;pwd=:P;server=theserver;initial catalog=thedatabase;MultipleActiveResultSets=True;Use Encryption for Data=Optional;MARS Connection=True;

The application will run fine for weeks and suddenly will start throwing "The 'MSOLEDBSQL19' provider is not registered on the local machine." at System.Data.OleDb.OleDbConnection.Open().

Obviously it's registered so the message is misleading. Once the error starts happening it will happen for everyone. I quickly swapped in "sqloledb.1" for "MSOLEDBSQL19" and refreshed the app pool and got it working, but I know that "sqloledb.1" is deprecated.

Any suggestions? Is IIS running out of connections? Is it because there's a 32-bit driver also installed and it's getting confused?

Windows Server 2019 Datacenter (OS Build 17763.8389) on Azure, IIS 10.0.17763.1, app pool has all defaults except .NET CLR Version is v4.0 and Load User Profile is false. Installed driver is 2019.0192.0000.00

Erland Sommarskog 133.1K Reputation points MVP Volunteer Moderator

2026-02-17T21:49:21.4966667+00:00

Any particular reason you are using OleDb Client rather than SqlClient?

Were you able to get it working again with MSOLEDBSQL19 after restarting something? Or it is it permanently broken?

By the way, I note that you have both MultipleActiveResultSets=True; and MARS Connection=True in the connection string. They mean the same thing, and only one of them has actual effect. But then you said that you were able to get things to work with SQLOLEDB which does not understand MARS. That suggests you may not need MARS at all. If so, I would recommend to remove MARS entirely, as it comes with some performance penalties with large result sets.
Akhil Gajavelly 1,570 Reputation points Microsoft External Staff Moderator

2026-03-05T07:11:28.5866667+00:00
Hi @David Weigel ,

Since the provider works normally for weeks before the issue appears, it is unlikely that the driver is actually not registered. This behavior can sometimes occur if the IIS worker process fails to load the OLE DB provider after long uptime, app pool recycling, or a bitness mismatch.

You may want to check the following:

Ensure the IIS Application Pool bitness matches the installed MSOLEDBSQL driver (Enable 32-Bit Applications setting).

Check whether the Application Pool recycled around the time the issue started.

Review Windows Event Viewer for any COM or provider loading errors.

Restarting the Application Pool or IIS may temporarily resolve the issue by reloading the provider.

Also note that MultipleActiveResultSets=True and MARS Connection=True are redundant, so you may only need one of them.

Thanks,
Akhil.
Akhil Gajavelly 1,570 Reputation points Microsoft External Staff Moderator

2026-03-11T04:42:31.38+00:00

Hi @David Weigel ,

Just following up to check if you had a chance to review the suggestions shared earlier. Please verify the IIS App Pool bitness, recycling behavior, and check the Event Viewer for any provider or COM-related errors when the issue occurs.

Let us know if the problem still persists or if you were able to identify the cause.

Thank you,
Akhil.

1 answer

Your answer

Erland Sommarskog 133.1K Reputation points MVP Volunteer Moderator

2026-02-17T21:49:21.4966667+00:00

Any particular reason you are using OleDb Client rather than SqlClient?

Were you able to get it working again with MSOLEDBSQL19 after restarting something? Or it is it permanently broken?

By the way, I note that you have both MultipleActiveResultSets=True; and MARS Connection=True in the connection string. They mean the same thing, and only one of them has actual effect. But then you said that you were able to get things to work with SQLOLEDB which does not understand MARS. That suggests you may not need MARS at all. If so, I would recommend to remove MARS entirely, as it comes with some performance penalties with large result sets.
Akhil Gajavelly 1,570 Reputation points Microsoft External Staff Moderator

2026-03-05T07:11:28.5866667+00:00

Hi @David Weigel ,

Since the provider works normally for weeks before the issue appears, it is unlikely that the driver is actually not registered. This behavior can sometimes occur if the IIS worker process fails to load the OLE DB provider after long uptime, app pool recycling, or a bitness mismatch.

You may want to check the following:

Ensure the IIS Application Pool bitness matches the installed MSOLEDBSQL driver (Enable 32-Bit Applications setting).

Check whether the Application Pool recycled around the time the issue started.

Review Windows Event Viewer for any COM or provider loading errors.

Restarting the Application Pool or IIS may temporarily resolve the issue by reloading the provider.

Also note that MultipleActiveResultSets=True and MARS Connection=True are redundant, so you may only need one of them.

Thanks,
Akhil.
Akhil Gajavelly 1,570 Reputation points Microsoft External Staff Moderator

2026-03-11T04:42:31.38+00:00

Hi @David Weigel ,

Just following up to check if you had a chance to review the suggestions shared earlier. Please verify the IIS App Pool bitness, recycling behavior, and check the Event Viewer for any provider or COM-related errors when the issue occurs.

Let us know if the problem still persists or if you were able to identify the cause.

Thank you,
Akhil.

Answer 1

The error message "The 'MSOLEDBSQL19' provider is not registered on the local machine" can be misleading, especially if the provider has been functioning correctly for an extended period. Here are some suggestions to troubleshoot and resolve the issue:

Check for Driver Conflicts: Since you mentioned that both 32-bit and 64-bit drivers might be installed, ensure that your application pool in IIS is configured to use the correct bitness that matches the installed driver. If your application is running in a 64-bit mode, ensure that the 64-bit version of the MSOLEDBSQL driver is installed and being used.
Connection Limits: Investigate whether IIS is running out of available connections. You can monitor the number of active connections and the connection pool settings to see if they are being exhausted.
Driver Reinstallation: Sometimes, reinstalling the driver can resolve registration issues. Ensure that you have the latest version of the Microsoft OLE DB Driver for SQL Server installed.
Event Logs: Check the Windows Event Viewer for any related error messages that might provide additional context on why the provider is failing.
Application Pool Recycling: If the application pool is recycling frequently, it might lead to temporary issues with the driver registration. Consider adjusting the recycling settings to see if that helps.
Update the Connection String: If you continue to face issues, consider using the sqloledb provider as a temporary workaround, but plan to transition back to MSOLEDBSQL19 once the underlying issue is resolved.

By following these steps, you should be able to identify the root cause of the issue and restore functionality without relying on the deprecated provider.

References:

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"'MSOLEDBSQL19' provider is not registered", but it is, and runs fine for weeks

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