Why won't my winged steed of the Ebon Blade work?

[Itsdangus]

So I made a DK and i'm currently lvl 79 in northrend trying to progress to icecrown but I realized I need flying to really do the content.
So I grinded for ages to buy lvl225 riding and saved the gold for the mount, but even in outland and northrend I can't cast it and use it at all?
It doesn't light up like my other abilities and I'm confused as to why I can't use it?
Any help would be greatly appreciated, thank you.

P.S. It just says "You can't use that here" even though I'm literally in Storm peaks???

[Dozorto]

did you buy northend flying? It's a license required to fly in northend, bought in dalaran/borean tunrdra (1kgold)
Buy other mount to check if you can fly at all
as a temporary solution, get a free k3 mount (for use in st.peaks, icecrown, schola)

[Itsdangus]

wow thanks heaps man, really appreciate the help!