Tab S2 not recognizing external hard drive after Marshmellow update

[AC Question]

I have a 640gb external hard drive I used to save documents & pics from my old Windows 7 laptop. I could access the files on my Tab S2 using an OTG cable & also back up files from my Tab S2 to the external hard drive. After Marshmellow it no longer accesses this hard drive and says it is corrupted. Does anyone know if there is a setting that can be tweaked or something? Or does the external hard drive need to be reformatted from scratch to work with Marshmellow? Thanks in advance for any suggestions.