That is strange indeed. The only thing I can think of is what sometimes happens to me in DA2 - sometimes my selected character stops responding, and their portrait is "shaded" slightly. When that happens, clicking on the portrait that is "shaded" in this way gets things working normal again.
Don't remember it happening to me in DA:O though, but you might just want to try clicking on the charcter portraits, and then trying again.
Also, try restarting your computer - sometimes if things get really screwed, restarting just the game may not do the trick.
If you can't get it to work, then you might want to contact EA support - either that, or try un-installing and re-installing the game. I think it SHOULD preserve your saves if you uninstall, but you might just want to go to your save folder, and copy the contents somewhere else, so that you don't lose your saves.