Ok so I found Alethius' journal and I'm in front of a giant spider web (the ones you normally just hit a few times and get through) I've spent 10 minutes hacking at this thing and casting fire spells but I can not get through it. Has anyone done this quest yet? It's a side quest you get while following the Thieves Guild quest line in Understone Keep. Any help would be much appreciated

I just it the right portion with one fire spell and it broke away and then when I tried hitting the left portion nothing happened, so maybe try hitting the other side of the web.

Got the same problem, and solved it. Position yourself to the right side of the web, and you'll be able to hit it. It is a very irritating bug though, and it wasn't until my third try at it(20 hours of gaming later) that I managed to get through.

Hope it'll help!