When you use the Microsoft ODBC Driver 11 for SQL Server in a multithreaded application, a connection attempt (SQLDriverConect/SQLConnect) results in an access violation.
This issue occurs because of a race condition that is caused by an oversight during initialization. When two or more threads try to create connections, the issue occurs.
Cumulative Update information
The issue was first fixed in the following cumulative update of SQL Server:
Each new cumulative update for SQL Server contains all the hotfixes and all the security fixes that were included with the previous cumulative update. We recommend that you download and install the latest cumulative updates for SQL Server:
To work around this issue, use an application that can establish the first connection in a single thread. If the first connection is established in a single thread, the SQL Server Native Client 11 driver (that is, the earlier ODBC driver version) won't be used to make the first connection attempt. This avoids the issue.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.