bugs Quest items are invisible after installing Dawnguard

I just installed the Dawnguard DLC (I play on PC) and I've already noticed a major bug. For whatever reason all of the quest items I have in my inventory are now invisible, when I say invisible I don't mean gone, they are still there, they just dont show up (I know this because I have the weight from them). I noticed this bug while I was doing the dark brotherhood quest breaching security. I killed Gaius Maro and went to plant the incriminating letter on his body but I could not find it anywhere in my inventory. I tried using the console to get another one but even though it said "incriminating letter added" the item still didnt appear in my inventory. Then I used a command to put the letter in Gaius Maro's inventory and it was visible there (the objective didn't complete though). I tried taking the letter from his body but even then it didn't show up in my inventory. However, it was definitly there as my weight increased. Then I looked through my inventory for other quest items and realised all of them were'nt there. If you are having this same issue or know a fix please post.



Thanks in advance.