Can not progress past chapter 3.

RyansPrivy

I sided with the shadow thieves. Paid my 20,000 to Gaelen. But can not open door to Aran Linvail lair. Can someone help?

lunar

Gaelen gives you a key to open that door. Check around if you dropped it somewhere. If you misplaced it, enable the cheat console and add the key to your inventory via AddItem cheat. Alternatively, use eekeeper and give the key to your inventory. Its code is MISC4S IIRC, it is 'shadow thief cellar key'

CLUAConsole:CreateItem('MISC4S')
should work as a cheat
(You should first enable the cheats from baldur.ini file in your game folder. Google it to see how.)