Here's an example-- I was walking to Riften and on the way I hit stage 4 vampirism. The guard at the outside of the gate didn't mess with me and I even stood directly in front of him to be sure. Then when I entered, both guards proceeded to beat the crap out of me. Reloaded twice and got the same result every time. Is anyone else having this happen after installing Dawnguard? It says on TESWiki that after installing DG the only time NPCs should be hostile towards you is when you're in Vampire Lord form.

I had that problem once in Solitude, I got into Stage 4 as soon as I fast traveled there and the guards seemed to notice that. I took a blood potion and they stopped, but I noticed that if you enter the 4th stage in a place where no one can see it (in a dungeon or anywhere outside of a city), no one should attack you. I was in the 4th stage for about a week in-game and I wasn't attacked once.

Yea. Since becoming a VL, the only time I dropped from being a stage 4 vampire was when I had to feed on the dude to make him a vampire. The entire rest of the time I've been walking around as a stage 4 VL without getting attacked by anyone. That's a good thought about reaching stage 4 when noone's around. I can't confirm or anything but that very well may be the case.

Interesting, Venule... I'll have to try that out the next time I play. I did hit stage 4 in front of the outside guard in Riften so that could have been it. What confused me was that he didn't attack me, but the guards inside the city did.

Never had any problems with guards or any other NPCs. Even once I was in Whiterun, inside the blacksmith house during Vampire Lord transformation and he was just watching me. I had to go off and back on the Vampire Lord transform, until he attacked me.

Did you have a bounty on your head in Riften?