It seems every vampire tells me to speak to vingalmo for my next quest, yet all he has is the 'not to be trusted' topic for the other vampire. I dismissed this issue thinking id come back later and he'd have the topic, but now i cant even revert back to an earlier save. Now im stuck with a broken side quest-line. Is there any way around this?

I haven't found one yet. I had to restart my character for a different bug issue then ran into this one. REALLY irritating.

I am having this issue also

Vingalmo gave me a quest to turn Validor in Riften into a vampire after I already turned him into one. So I did the only logical thing (since I could not reload by that point), I killed him. It seemed to fix the quest-bug and net me 100 gold in inheritance. These quest-bugs should not be happening.

The same thing happened to me, except I keep getting the quest to turn Cairine in Markarth into a vampire and can't complete it a second time. I wish they would hurry up and fix these quest bugs too.

It's really best to save your game before entering Castle Volkihar and getting a new quest, it would appear which quest you get is decided randomly, I once got the quest for the Blood Rings, but one of the rings spawned in The Katariah, so I had to reload quite a few times, to get it again, and for it to spawn in another desirable location...

This is the best solution.

I've re-started (for the 2nd time) my newest vampire character and have taken to getting quests and then forgetting them. So far they don't seem to glitch up unless the quest location becomes the location for another quest (see especially the Lost Legends quest). I've also taken to completing the objectives for the quest but not returning to the Castle, which has done well in allowing me to do stuff outside of Vamp quest lines.

But always, always save before entering the castle so you can change the new quest if need be.