I have a portable Arduino IDE version 1.6.5 set up, and have used it for years.
Not so recently however.
I tried compiling an old sketch that uses/needs 1.6.5, and got this
toss165Cant.ino:2:20: fatal error: Servo.h: No such file or directory
I looked in the Arduino 1.6.5 package. I saw the Servo library. I removed it, and used the IDE to install a servo library.
It went into my Java/portable/sketchbook/libraries folder. But still was not found by the compiler.
I thought that would do. Just in case I moved the Servo folder into Java/libraries as a stab at the dark. No joy.
Yes, restart IDE between these steps.
The IDE knows where to put the libraries, but not where to find them?
More: I downloaded the Arduino IDE 1.6.5 zip and set up a new portable instance. I changed the file permissions of the entire installation to wide open for everyone after adding the Java/portable folder.
Launching that IDE gives an error dialog
Arduino cannot run because it could not create a folder to store your sketchbook
Something I will follow up on, in the meantime tell me I am missing something ovbious.
Recipe for portable, my notes after finding how here. Some time ago.