Invalid Characters for Box Upload

It's not a huge issue, but FlipaClip's of the '+' symbol to denote spaces in filenames when exporting PNG sequence results in an 'Invalid characters in Filename' error when uploading to Box.com.

I often use Box.com for transferring files from tablet to PC, so I have to try to remember to not use spaces in my filenames - I don't always succeed!  Maybe replacing spaces with a dash or underscore might be preferable?