Spacemacs - 'Cannot make side window the only window'

I like using neotree, SPC-p-t, and I rely on it to open, rename, move and create  files.

The other day I tried to create a new file and got an error, "Cannot make side window the only window"

It turns out that it is easily fixed using SPC-f-e-R or spacemacs/reload.  This will reset the layout of all the frames or the layers or something, but the bottom line is it fixes the problem and now I can make new files with neotree.