2003 Mercedes Benz 430e Trunk release malfunction

Why doesn't my trunk open when when I activate the inside trunk release switch or press the trunk release on my remote key?

The trunk will not raise up when activated with the remote key or the interior trunk release switch. I installed new batteries in both remotes and this does not make a difference. However, I can hear a click inside the trunk when pressing the trunk release on the remote. When I open the trunk manually it is hard to raise up. However when I press the red closure switch on the inside of the trunk it closes as it should.