"System extension cannot be used" after installing iTunes 11.4
Installing latest version of iTunes (11.4) today led to the following error message:
System extension cannot be used
The system extension “//System/Library/Extensions/AppleUSBEthernetHost.kext” was installed improperly and cannot be used. Please try reinstalling it, or contact the product's vendor for an update.
I'm able to use my USB drive for Time Machine, and that appears to be functioning ok. Why this error message? Anyone else had it? And what does it mean for the continued safe operation of my MacBook? Would be reassuring to know if this is happening for anybody else, and if anyone else has found it affecting them. (Other than the distraction of getting a worrying error message that I take time out to report?)
Thanks in advance.
MacBook Pro, OS X Mavericks (10.9.4)