This error indicates that the iSCSI target closed the underlying TCP connection.
Check that there are no duplicates of the IP address of the initiator on your network.
Check for license issues of the target server.
For StarWind, the log will contain an entry similar to:
10/25 15:09:36.529 be4 Srv: *LICENSE* Rejected connection to 127.0.0.1:3260 from
192.168.1.223:41381. Maximum of 2 allowed clients already connected to the server!