File Exists error after upgrade to node-red 3.1.1 (from 2.x)

The resolution of this problem, for me, was that I forgot to add in
'fs' : require('fs')
to the settings.js file. Once I did this, the errors went away.

What I'm trying to do is create a file with a date in the file name. Everything logs to a file WITHOUT a specific date in the name, but just after midnight I rename the previous days file to a name with the date in it, and create a new file with a new header.