I have completed Dawnguard, I want to get the spell conjure mistman and when im going to soul cairn i cant enter and it drains health.
Im a werewolf and when i transform in a vampire i can enter but i want to be a werewolf
First I have transform in a werewolf by the companions then i've transformed in a vampire and then i use the oportunity of aela and to be a werewolf again
How can I be a werewolf again if i will transform in a vampire?
Or there is another way to enter in soul cairn?

I can't enter the Soul Cairn again, neither as vampire or as human.

All we can do is to scream really loud on the support-forums and make sure that people become aware of this problem so that it can be patched in a future patch. Other than that, I can't help.

I have doubts screaming loudly will accomplish much, you have to re-enter the Soul Cairn on the same forrm as you left it. You went and changed into something else once you left, I would think your Soul Cairn travelling days are over. If you went as a vampire, and got yourself cured or turned into a werewolf you could try asking Serana to change you into a vampire. But Aela will only give you one second chance at being a werewolf. If you were not a werewolf when you entered the Soul Cairn the first time, I doubt anything you do will be getting you in there as a werewolf.

I know the op used less than appealing grammar, but you essentially just repeated everything he stated. Also, from comments made by Valerica, it is clear that you SHOULD be able to re-enter the Soul Cairn in any form upon exiting, but obviously that feature is not working as intended (among several others in all honesty).

I've said this before, and I promise I'm not doing it to brag, but I had this exact same problem and I was able to have Serana turn me into a VL after having regained my lycanthropy and I WAS able to re-enter the Soul Cairn. Why this worked for me and not for either of you, I don't know, but I do not doubt that when (or I suppose if, a depressing thought if their ever was one) they patch DG, they will fix this issue.

This

I have a hard time believing that curing vampirism would lock you out of the Soul Cairn, especially since we actually paid to get there in the first place :/

And on top of that, my character can't return in either form, so it is obviously something wrong that needs to be fixed. And Valerica implies that the player should be able to return in either form, so yeah, something is still wrong.

I dont kwow what says valerica
when I was there, i asked her and apears some numbers and letters in the subtitles and she dont say nothing
there are a lot of bugs, I hope that in the next patch will fix all

I was able to return to the Soul Cairn yesterday through the castle bridge entrance. The mistake I almost made was while walking around the spiral entrance I was hitting the (A) button to enter, and nothing was happening, then I realized I had to walk into the spiral. (Brain fart) I was returned to the Soul Cairn without any problems.
I have cured being a vampire, so I'm not sure if that makes any difference. I also had Serana with me again.
I discovered many quests that I missed on the first visit to the Soul Cairn. I also got the Conjure Mistman Spell, which is really great since I can conjure twin souls.
I also talked to Serana's Mother again, and told her I killed Harkon, she thanked me and returned to the castle.

Hope this helps, but if you can't return that's a shame because there is many hours of new gameplay inside the Soul Cairn.

I suggest you try to cure yourself of being a vampire, and try again.

Good Luck.

I returned with no problems & talked to both the mom & the dragon again. I didn't know there was another spell I could learn there. I haven't ever been anything but a high elf, except for the short werewolf period during the Companions quests.