It's to do with how the keyboard is wired and the micro controller inside it. Most keyboards are wired so that certain key combinations will prevent other key presses from being detected by the keyboards micro controller.
Under such circumstances the only things you can do are:
1) Try another keyboard.
2) Change your key bindings to new keys, check if you can use the new key bindings properly, if not then repeat the first step and change the key bindings again.
