The subject behavior can occur under heavy load, because the high activity is incorrectly identified as a denial of service attack.
To workaround this behavior, turn off the new denial of service detection:
1. Open a CMD.EXE window.
2. Type the following command and press Enter:
REG ADD HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters /V SynAttackProtect /T REG_DORD /F /D 0
3. Restart the server that is running SQL Server.