...is still a fairly simple raid...
here is how to screw it up.
1) Don't understand builds.
-Yes ladies and gentlemen, not understanding builds is the first step in screwing up an epic raid. I would go into detail...but in short, expecting a 16 bard/2 fighter/2 barb to scroll heal someone on a base is probably a really really stupid idea. The umd is most likely for self healing since the 6 second cooldown and no evasion can make it extremely difficult to keep someone up while not dying.
2) Assign people to bases where they cannot fulfill their duties.
-This includes, but is not limited to, sending a caster to third base while having 2 people continue from second to third to finish the base without a divine...only a bard. Common sense would lead most to believe that if a caster cant solo it all the way, then you send everyone in the same fashion as the first 2 bases. Also, when you're on a dps toon and you are taking a bard onto the last base with you...you probably shouldn't make the bard go in first. You see, what happens is the bard will then take the first hit of damage, and when they have to use a heal scroll to not die, it puts their healing capability on a 6 second timer. Also note that scroll healing requires a concentration check vs incoming damage. A non-evasion toon will have to roll incredibly high to succeed. If they fail the first scroll to self heal, then you are waiting 12 seconds for the dps heal.
3) Do not understand strategy
-This is probably the best way to tank this raid...and I'm not talking about holding aggro. This point can be visited in #2 up above somewhat. But there is a major problem that has been introduced recently, eggs. Eggs will make your life very unhappy very quickly. It might seem like a wise idea to try to brute force velah down before the eggs hatch...but it's a bad idea...a really really really stupidly bad idea. It takes a matter of 15 seconds or so to clear the field of eggs. Designate a tank, split the melee...omg that was hard.
I hope you have found this guide to be useful. I wish you the best of luck in wiping your future raids.