Can't spend souls to buy shouts!

[Raczoon]

I select I word I want to gain, chose to spend soul, the OK/Cancel prompt pops up, I click OK. The box then goes away, and I don't gain the word, or lose any dragon souls.

How can I fix this?

 

I've put up with this problem for a while, but now I'm stuck on Dragonborn, because I need a shout in order to do the questline.

Lvl 40 something, still only have what Greybears gave me :-/