Assume that you are using Microsoft SQL Server 2016 and 2017. When you run the sp_set_session_context stored procedure repeatedly (for example, more than 10 times) to set the KEY value parameter with a NULL value, you may receive an error message that resembles the following:
Msg 15665, Level 16, State 1, Procedure sp_set_session_context, Line LineNumber [Batch Start Line LineNumber ]
The value was not set for key 'KeyName' because the total size of keys and values in the session context would exceed the 1 MB limit.
This issue is fixed in the following cumulative update for SQL Server:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Learn about the terminologythat Microsoft uses to describe software updates.