Glitches and audio dropouts on Mixdown when copying to shared folder

Here’s the scenario:
I am using Cubase 5 (pc version) with a saffire pro40 interface. I decide to do a mix of a project I’m working and mixdown a stereo file to my studio pc, which plays fine with no problems. I then copy it to a Dropbox folder so it can be accessed on other devices, but when you open the file from say an iPhone the track has various nasty glitches and random audio dropouts. Most strangely of all, the midi drums on the track disappear after about 4 bars and never come back!
It seems like it’s an issue when transferring files online, but I’m just not sure.
Any advice would be appreciated.