Unable to do the Unholy Infusion quest.

There is no need to bump a thread while it remains on the first page, Shieldd. :)

Are you in the 25 person ICC?

It appears that you have become the abomination according to your screen shot.

Did you get to phase two and use the Infuse ability? I believe that costs 100 energy to do but once you enter phase two you should have the option. After that you'll receive a 6 minute buff. Did you then kill the Putricide within those 6 minutes

Edit: Taking another look at the screen shot it doesn't appear that you have the ability for the Shadow Infusion available to push.

I assume you had the quest in your quest log at the time?

You will also want to make certain that you have Shadow's Edge equipped before you enter the abomination. If you equip it after you enter the button won't appear.

Beyond that my best guess is that there is either an addon interference or a corrupt file. You could try resetting your User Interface or even running the Repair.exe file which is located in your Worldofwarcraft directory.

http://us.blizzard.com/support/article.xml?locale=en_US&articleId=20377

Q u o t e:
Yep, the button didn't appear and I equipped it.

You equipped Shadow's Edge while you were using the abomination or you had Shadow's Edge equipped before you entered the vehicle?

Q u o t e:

Turned off all addons except for DBM, which wouldn't effect it.

Turning off addons is not the same as returning the UI to default, addons can do many strange things even ones you wouldn't imagine.

Q u o t e:
Ran the file, this is the ONLY bug I've had, and this is the 3rd time I've had this problem. We really need to get this fixed.

Unfortunately, Shieldd, we've receive no other reports of an issue with the quest and without standing over you while you are doing the encounter it is difficult to verify if there is something that you may be doing or not doing that is causing it or if there is an actual issue with the encounter. Our Quality Assurance team, which investigate these reports, wouldn't have anything to go on to try and reproduce this.

My best advice would be to reset your User Interface, return it to default and do not load any addons until after you complete this encounter. it is important to eliminate a UI issue as a possible source of the issue. Then, with Shadow's Edge equipped well before you enter the vehicle, give it a try.

Again, Shieldd, turning off or disabling your addons is not the same thing as returning your User Interface to default.

As Pahanda said, if you run the encounter without any addons and still experience the same outcome our Quality Assurance Team may be able to look into it further.