I was searching for an answer to the same issue. I was getting errors when trying to stream music from my Dropbox over 4G. "File Type Not Supported" was the main error message.
I never received this error when streaming over WiFi.
To correct this, I simply went to my default music player (Play Music by Google) and unchecked the Download Via WiFi only box.
I know that some of you will have far more elaborate answers to this question, but this worked for me.
I have the new HTC One. (Love this phone)