Found a bug in Lightroom 5.5 for Windows:
"Can't move folders into their own subfolders"
I have a folder named, "2010". I created another folder in the same level as "2010-2019". Attempting to move "2010" into the new "2010-2019" folder results in the below error. Rename to "a2010-2019", then moving 2010 into the new "a2010-2019" folder works. After that, I renamed "a2010-2019" back to "2010-2019"
Error: "Can't move folders into their own subfolders"