Right after you talk to the doorlord your supposed to be let into the tunnels. But in the GoG version I am unable to enter the tunnels. Anyone else have this problem and know how to solve it?

Could you be specific on what exactly happens? Do you get the right dialogue; afterwards no cutscene showing Boots and Grumps jumping over the railing?

I get the cutscene showing them jumping over the rail, but the entrance to the tunnels are blocked by grates where your supposed to enter.

The problem may lie in where you think the access to the tunnel is. Under the bridge, below the door guard, there is an opening to the Mystech Tunnels. Indeed, it is very dark so it is understandable why someone could overlook it.

[url=]http://www.youtube.com/watch?v=0q88wgl3t3g&feature=share&list=PL2D6265063CCF0689[/url]
Around 8:15. You can see him having trouble finding it as well.

If there is a grate at that entrance as well, I'm absolutely baffled. It wouldn't make any sense if it was there.

Hopefully this helps.