The problem turned out to be extraneous HTML code in the description for the organization, which brings up a good point...
When writing descriptions of things in ArcGIS Online, whether for items you add, web maps you create or even your organization's description, it's best not to copy text from existing web pages. You get a lot of extra HTML code that you can't see. If you do want to copy text from a web page, paste it into Notepad first, which will strip off all HTML.
Mike