I've experienced something similar to this but it was with armor, I think. It's been a while...
In my case it turned out there was a valid reason and I just didn't understand the rules of the game. I should point out that the game did not try to help me understand but, instead, simply refused to allow what I was trying to do. It would be nice if a message came up somewhere telling me "you can't do that because...reason".
You might need to provide more info for people to help you out on this one. There may have been some in-game condition you were suffering from that prevented you from doing what you wanted or it could have been a bug. The more info about your character's condition you can provide the better.
