Why am I being told I can't use my iPod when I clearly am?
Solution 1:
So your problem is just the error message?
This thread seems to state that only USB HDDs can be used:
I think it only works with straight USB flash drives. If you are using an external HDD as a main storage unit, I'm not sure it will work. One of the reasons is the PS4 is only going to recognize USB drives up to a certain storage max.
Perhaps this is why you are getting the error message.
You could get rid of those error messages if you connect the ipod to a computer running a media server, and then connect from the ps4, as outlined in this article