Microsoft SQL: A connection was successfully established with the server, but then an error occurred

HI LucianoS ,

If you're getting this error after January 2022, possibly after migrating from System.Data.SqlClient to Microsoft.Data.SqlClient or just updating Microsoft.Data.SqlClient to version 4.0.0 or later, it's because MS has introduced a breaking change::

https://docs.microsoft.com/en-us/sql/connect/ado-net/introduction-microsoft-data-sqlclient-namespace?view=sql-server-ver15#breaking-changes-in-40

Breaking changes in 4.0

Changed Encrypt connection string property to be true by default.

The default value of the Encrypt connection setting has been changed from false to true. With the growing use of cloud databases and the need to ensure those connections are secure, it's time for this backwards-compatibility-breaking change.

Ensure connections fail when encryption is required

In scenarios where client encryption libraries were disabled or unavailable, it was possible for unencrypted connections to be made when Encrypt was set to true or the server required encryption.

Rick Strahl has posted a detailed explanation on his blog

The change was made in this SqlClient pull-request in August 2021, where there is additional discussion about the change.

The quick-fix is to add Encrypt=False to your connection-strings.

Similar question refer:

https://stackoverflow.com/questions/17615260/the-certificate-chain-was-issued-by-an-authority-that-is-not-trusted-when-conn

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Best Regards

Lucien