Since Arduino 1.6, the libraries path not only available in Arduino default path installed (\Program Files (x86)\Arduino\libraries), there is another path to be considered.
Yesterday, I got an error caused by same multiple installed libraries but different path name. Between LiquidCrystal library and NewLiquidCrystal library.
The compilation got an error like,
Multiple libraries were found for "LiquidCrystal_I2C.h"
Not used: C:\Users\Administrator\Documents\Arduino\libraries\LiquidCrystal
but it not give any problem and able to continue its compiling process and upload to device.
In Arduino IDE 1.6, user able to add, manage and download specific library user wants. The problem is, once installed, there is no way to remove the library. So, above error might occur to some users.
One way to remove the "Not used" library is to look it at path c:\Users\Documents\Arduino\libraries\
Some customs libraries are in there. Some might duplicated with in \Program Files (x86)\Arduino\libraries or in C:\Users\Administrator\Documents\Arduino\libraries itself.