Can't make new folder in my external hard drive
I can't seem to create new folder on my external hard drive. I'm using WD external hard drive.
What could be the problem?
I probably should have asked a second question - is this a new drive or has this problem just developed? Most external drives are shipped ready to use by Windows users so they are formatted with NTFS which Macs can read but cannot write to without 3rd party software. If it is a new hard drive with nothing important on it, check out this help article: Format external drives to Mac OS Extended before using with Aperture - Apple Support
Ignore the "before using Aperture" comment. This is how you prepare a drive for the Mac.