I'm having the exact same issue when trying to translate an article from English to Portuguese. The messages change back and forth between "All capital letters" and "Improper content and / or summary related to the human body." The error message doesn't highlight any text whatsoever, even though it usually highlights the paragraph in which the error occurs. I've read the entire article several times looking for instances where there may be an issue, but found none. It's been extremely frustrating trying to translate articles using this tool.
It also gave me the "all caps" error when adding an infobox, and the error only went away when I deleted the infobox.
For reference, I'm trying to translate this article: https://en.wikipedia.org/wiki/Sven_Väth