The issue seems to be that when using this plugin, Unity needs to use the java compiler (javac.exe) But it’s not found in the C:\Program Files (x86)\Java\jre7\bin\ folder.
You must install the JDK and set the JAVA_HOME environment variable to C:\Program Files\Java\jdk1.7.0_45
You must also add the jdk bin folder to your PATH: C:\Program Files\Java\jdk1.7.0_45\bin
You must then reboot.
That did it for me.
forget everything just go to C:\Windows\SysWOW64 and paste java.exe from C:\Windows\System32 or anywhere from your jdk path like :- C:\Program Files\Java\jdk1.8.0_20\bin