I came across an issue the other day when on my Iphone 5.1 the twitter application could not save a picture to the photo library. Kept prompting me to give access to twitter to the photo library.

Many forums and blogs said to change the privacy in settings, but there is no such setting on 5.1.

Turns out I had to set the Location Services within the Settings and turn on the Twitter option. Somehow I had turned this off earlier. Seems strange that location services needs to be on to save the picture but I believe that when the picture is saved the photo library uses the location as meta data and it couldn't do this.

Now fixed. For those that have the same issue.