Here's an update on the situation:
Don't embed youtube videos in a post without first inputting text above it!
So Write some text....then embed!
Should you paste an embed into a post without first putting text above, that move will trigger or, at least has previously triggered a bug that produces the below error. What occurs after that is a disabling of your posting option on your browser until you delete the cache (delete history etc (specifically form). Firefox has continued to display the issue on my side regardless of deleting my previous history!
Do not experiment with a browser you use often lol
Hope this saves some of you from this irritating and Steemit debilitating bug.
Take Care!