This is the first time I have experienced this issue and am hoping for a simple fix. My Orc is level 45 and has just arrived at Castle Volkihar for the first time with Serana (who is following me closely). The gate keeper opened the metal gate and announces "Is that you Serana? Serana has returned" or something to that effect, but the wooden doors wont open.

I took the jetty to the island, walked slowly up road to the castle doors with Serana and waited for her to give me the "When we get in there....." speech but still unable to obtain entry. I've tried waiting 24 hours, fast traveling to other locations and returning days later, and even loaded an earlier save when I was level 42 (now level 45) and going through the entire quest again where I find/meet Serana and still cant enter. Could it be due to the fact that I am also a werewolf?

Any help, tips, advice is greatly appreciated.

Again, I tried all of the following with no luck:

Waiting 24 hrs
Fast traveling away
Reloading earlier save (3 levels below)
Going through the quest to rescue Serana again

Interesting...

Usually reloading the previous save works just fine to get the glitch to clear up, but I see you've already tried that. I'm going to have to think on this one.

Im starting to think that maybe I need to cure my being a werewolf first? Or, I hate to do this, but maybe I need to go back and reload a save from when I was in the 30s level. Ugh. Hate to do that.

Sounds like that's just bugged to me because every save I've done with joining the vamps you walk up to the castle serana says before we go in ect, the gatekeeper says... I'm just the gatekeeper then you go walk inside an vingalmo is standing there an says how dare you bla bla... Wait serana is that you... Everyone serana has returned.

I've never had that dialog before entering the castle, only after I entered the castle.

Well, it's not the Werewolf that's the issue as Harkon's Gift can overcome that. It may be if you keep your current save intact, but delete and then reinstall Dawnguard, that may work.

And this is perfectly safe for your Save Files, btw.

You may have to go through the lvl 30's load again...

Some people the fix was deleting the character and starting from a new file (The corrupted file for whatever reason carried over to the other files), or uninstalling both dawnguard and skyrim.

I don't recommend any of these unless you get direct help from Bethesda lol.

But last I heard, people looking for direct help from Bethesda, it took them like 3 weeks to tell them to uninstall their games.

My werewolf character got in without any problems. Nothing you did before going to Dimhollow Crypt should affect getting into that castle, and it seems like you have done it with other characters. Save when you first enter Dimhollow, before doing the puzzle to open the crypt where Serana is and another save before leaving Dimhollow with Serana. Replaying from one of those three saves should get you in. Try to do things differently, do not play the same way all the time. you have somehow set off a glitch with that one character, that beaks the door opening scene.

Since a few seemed to have the problem on both PC and Xbox 360, checking the forum for previous solutions might be an idea.