I can't access/save photos from/to my camera roll anymore

If you are an Android user, you have the option of specifying a default application to open photos or a default location to open from. If you change the option from “Just Once” to “Always” but didn’t intend to, you will always be frustrated. Fortunately, there is a way to change this on your phone that isn’t related to Pixlr specifically but that should clear up your issue: Go to Settings -> Apps -> Press Menu and choose Reset Default Preferences (or Clear Defaults).