In case this helps anyone else, I was having this problem, and it turns out for me it was because of a privacy setting. I had the setting "You can upload captures to Xbox Live: Decide to upload game clips & screenshots to Xbox Live" set to "Block." Changing it to "Allow" let me upload screenshots to the feed again. It would be great if there was an error message indicating this as a possible solution. Thanks!
David Whiteford
In case this helps anyone else, I was having this problem, and it turns out for me it was because of a privacy setting. I had the setting "You can upload captures to Xbox Live: Decide to upload game clips & screenshots to Xbox Live" set to "Block." Changing it to "Allow" let me upload screenshots to the feed again. It would be great if there was an error message indicating this as a possible solution. Thanks!