Sadly, I raised this bug in detail 4-5+ months ago with this exact error. It hasn't been fixed, and I have been trying the updates via steam in the vain hope it has been corrected. Well, it hasn't and continues to block my game, I haven't played in since and will not buy another Obsidian title ever again, regardless. In my opinion a bug this game breaking cannot go unfixed for any prolonged period, ever. DS3 was a far cry from 1 or 2, but due to the recent (back then) Obsidian titles that were pretty damn good, I decided to ignore the bad press and get it.....was quite enjoyable until this bug. So, uninstalled and the CD is now hanging in my veg plot as a 'scarecrow'. But hey, what do Obsidian care, they're developing new titles for the multi format gravy train which is killing PC gaming.
Sorry for the rant, but I cannot bear slack post sales support or multi platform titles for that matter, either.