iPhone does not like random music files? ...

I recently got a new iPhone, and it works perfectly so far, but it fails to hold asylum for music files properly.
No matter what I drag on there, 9/10 times I'll watch the loading bar at the top transferring the music files, once it hits a certain amount it'll freeze, and I get the process interrupted by an alert window saying Attempting to copy to the disk "iPhone" failed. The disk could not be read or written to.

My iPhone can sync contacts no problem, applications are no problem, calling or messaging people are no problem, but for some reason I can't drag select music files. The music files which seem to not want to go on there are completely random.
I'm trying to replace my iPod Touch, and I find it weird that the iPhone is giving me more problems than my Touch ever did.

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