Connectivity Error – A transport-level error has occurred when sending the request to the server. (provider: TCP Provider, error: 0 – An existing connection was forcibly closed by the remote host.)

It’s a connectivity problem with a previously opened session in SQL Server, Sometimes a user can get SQL server error as

Msg 10054, Level 20, State 0, Line 0
A transport-level error has occurred when sending the request to the server. (provider: TCP Provider, error: 0 – An existing connection was forcibly closed by the remote host.)

Some possible causes are as below

1. The server has been restarted, this will close the existing connections.
   
2. Someone has killed the SPID that is being used.
   
3. Network Failure
   
4. SQL Services restarted
   

RESOLUTION : Just hit F5 or (ALT + X) to re-run your query. SSMS will determine it is no longer connected and then prompt you to reconnect it will put you back into the same database.