Error upgrading firmware on Equalogic PS6100X - Unknown error 13 returned by the server

I am attempting to upgrade from firmware version 7.1.14 to 8.1.15 on a Dell Equalogic PS6100X.  I am using the 64bit firmware file.  I am getting "Unknown error 13 returned by server".  I can't figure out why this is happening.  I have also tried version 8.0.5 and get same error.