I can save files, but iTunes can't seem to

I have an external drive (My Passport).  I downloaded the drive so it’s properly recognized by my computer.  Then one day last week, my computer seems to have rejected the device.  I got an error message when I first logged on.  But I can still save files to the device.  iTunes can’t save files to it though.  I can see the device on My Computer.  When I go to the device properties/hardware it says this device is working properly.  When I go to tools, I click check now and nothing is found.  I unplugged all my usb devices and deleted everything using the device manager then restarted.  I still get the error message when I turn my computer on.   That the device was not properly installed and I could have problems.  And while I can save individual files on the device, my iTunes can’t save any files on it.  Any ideas?  Thanks! 

How are you saving the files from itunes to the drive?

To setup the drive as the storage you need to got through the settings on iTunes

check this for more info