Ha...and of course just after I posted this, I tried to upload again (after I just did another update and got the same result), and the error message is gone.
Apparently it's the "***** about it on the Adobe board, then it will magically fix itself" workaround.
Still looking for input on the start up display/missing project thumbnails.
Sorry to find you in this trouble, however, this issue should have been solved by the steps given in this doc - Some files on the server may be incorrect or missing which you said that already performed by you.
But if still not resolved then using this widget - Widgets for muse Shop which has also worked for many.
Let me know if this helps.
Thanks Ankush - figured out which library it's supposed to go in - is there a specific place I need to drag it in a project (just once in the master page, or every page?)