It doesn't matter if you first enter Dr Elrath's house before or after you have circumstantial evidence implicating him; either way he makes an excuse and leaves. You will meet him once more (briefly), but not until after you retrieve an item from his cellar. Make sure you explore and loot everywhere there first, since you will not be able to get back in afterwards.
The doors inside the house are controlled by something other than keys.... Spoiler :
The lanterns act like levers, and if you play a bit you should be able to get to the cellar. (highlight the text to read)Entering Elrath's house - screenshot with instructions
Is the crash when you talk to the manager again? Before fighting Bur'Leigh, try dropping most of your inventory, or stashing it in a chest. A couple people had problems either at this fight or with the dwarven king's guards with their inventory being returned, but eliminating most or all of the inventory beforehand avoided the issue.