To disable right click access in taskbar, in order to prevent users from accessing taskbar and start menu properties, starting task manager and adding any toolbars in taskbar, follow the below mentioned steps.
Goto “Start -> Run” and Type “gpedt.msc” (this will open Local Group Policy Editor)
In the left side of the editor, select
“User Configuration -> Administrative Templates -> Start Menu and Taskbar”
In the right side of the editor, Select “Remove access to the context menus for the taskbar” and double click on it.
Select “Enabled” and Press “OK”