Thanks Jimmy and Eric. Eric, my process for submitting directly was going to the YSE site feed page (rate.html), clicking "Submit Site Feed", selecting sitemap.xml from my local directory and clicking "Submit Feed." At that point I got the error message, "Sorry, your request is invalid." No other information was given. I have both an .xml and .html sitemap on my site.
I'll try resubmitting this evening, once 24 hours have passed since I last tried.