The error
I had posted the photo from my previous post through BeScouted.com, but when I viewed it here in Steemit I realized I had a minor typo in the URL to my photo website.
When I tried to edit the text and re-post I received a "Missing Posting Authority" error.
The suggested solution
I searched online to see if others had had similar problems and found a suggestion to clear all form fields, refresh the page, paste the contents in the empty fields and post. But still same error for me.
The solution
Having dealt with encoding issues in my own work before I suspected a character problem. I had used a "camera icon" character in the original text which showed up fine in the preview. After I removed it I could post again.
Just documenting this for future reference.
I tried to post this text with the same camera icon character but received the Missing Posting Authority error again - now trying without.
EDIT/UPDATE
I made an attempt to reply to this post with the offending camera icon. That attempt also failed. The screenshot is below to show what camera icon was used and that the preview was fine: