Your HTML cannot be accepted

FRUSTRATION CITY!

I've not been able to publish a post I recently wrote. This error message
keeps coming up:
Your HTML cannot be accepted: Tag is not closed:

Trying to locate the offending open-ended tag/font/what-ever, I've been going over the post with a fine-toothed comb. I can't find anything suspicious.

I even re-wrote the whole post in a new post window and did a 'fresh' re-link to all the links. Both the original and the re-write are currently 'in draft'.

Couldn't locate any fix-it advice about this in 'Blogger Help'.

Can anyone help?
(in techno-language lite ~ so I can understand)