Is this a bug? Why wont they surrender?

[Vesayen]

Im playing as spain and managed to siege, and beat the moors in spain.

When I go for peace and it gives me the "annex" option, the annex button is grayed out, why is this?!?!

[Ecthy]

odd

[Havard]

Do they have more than one province? You can not annex until they are down to one province...

[Apocalypse]

If they are down to one, make sure no allies are still in the war. If there aren't, then try waiting a month. Sometimes that fixes any problems.