Unknown Twitter error
Error Message: We're sorry for the inconvenience, but your tweet: [Tweet Content], sent from your profile: [Profile Name], did not post due to an unknown Twitter error. This was sent under the group: [Group Name].
If there was an image attached, ensure the size is within the limit, which is 1024 x 512 for Twitter.
Check out the recommended sizes of images uploaded via third-party apps by referring to this link.
You can also make use of Sprout Social's free online image resizing tool, Landscape (sproutsocial.com/landscape). There are custom dimensions you can choose from when you rescale your images.