A new problem just in last week.  Previously,   I was able to do

the " control A"method to select all messages in inbox, click delete, , and voila! - inbox emptied.

 Now just in the last few days, it won't work. I get a message "An ukn error has occured. Please try again." Frustrating! I don't think I've changed any setting on my computer, but what could account for this, please?