A transport-level error has occurred when sending the request to the server In our Vb.net application(userd within a local network connection inside a office), which is used from long time now some of the users get the errors only sometimes a day


  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.


I have already checked following


All databases are set to autoclose OFF
Didn't find much network problems and network speed is good.
When I checked in SSMS the under server properties remote query time-out set to 600 seconds
I checked sql server log and no errors found relating to it or same error message


So what may be the reason for this error? And how to troubleshoot it?
If an application opens a connection (successfully) to SQL Server, and leaves it open in anticipation of sending a (or possible 'another') query, and in the meantime, SQL kills that connection for some reason (eg, service restarts, or a kill command is sent), then when the connection (which thinks it's open) tries to send a command, you'll get this error.

So catch the error in your application, and reconnect. Then try the command again.