Taskkill /f doesn't kill a process
you must kill child process too if any spawned to kill successfully your process
taskkill /IM "process_name" /T /F/T = kills child process/F = forceful termination of your process
The taskkill and powershell (kill) methods didn't work for me; it still said "Access Denied".
I had better luck with this:
wmic process where "name='myprocessname.exe'" delete
Just had the same issue on Windows Server 2008 R2 and nothing helped, not taskmanager or taskkill. But, windows powershell run as administrator worked with "kill -id pid"