Cannot copy files direct from PC to DROID-Mini

[RandyIdaho]

Have direct connection to PC (Win7x64 OS) via USB data/charge cable. I am trying to copy MP3 files to the Music folder on phone but I get "Device might not be able to play this type of file", and then "Cannot copy file." I assume this phone can play MP3 files. I was able to create a subfolder in "Music", but cannot write to it or the main "Music" folder. The main reason I upgraded to this phone was bluetooth connectivity to my Sena motorcycle bluetooth wireless headset/intercom/phone system - mostly to play music. From what I can tell from the less than detailed manual, I should be able to copy files to the phone storage from a Win7 PC. Any help appreciated.