Why am I unable to use dragon souls to unlock dragon shouts?

I got the same message, but it turned out I was pressing 'E' to equip the shout, and not 'R' to unlock it.

If the shout you're trying to unlock is three words long, you may need three souls to unlock it.

You may have the wrong shout selected. Skyrim's UI is tricky sometimes, and you'll have a different menu item highlighted than you think.

Shout = word + dragon soul.

To get dragon souls, kill dragons.

To get words, explore. Look for dragon nests and for draugr tombs.

When you have both a soul and a word, you can unlock the shout by these steps:

• go to magic -> shouts
• select the word (should be greyed out)
• press the unlock button

You are pressing the wrong button. It's that easy. You are pressing the equip button not the unlock button. On PS3 it is square and on XBox its X. I don't know what it is for PC though. (It should be the same as your unsheathing button.)