Observed behaviour: force field blocking the stairs to level 2 is not dropping in spite of having all four wardstones and quest xp for removing the field being awarded.
Expected behaviour: open the bloody door!
Needless to say: this is a gamebreaking bug!
@CrevsDaak Can't upload a game now, going to work and writing this from my ipad but here's a screenshot:
Edit 10.2.2014: @MacHurto has posted a workaround further down - you need to keep clicking, some parts of the stairs will let you pass while the rest gives the errir message. It's still a serious bug though.