Message9990

Yes it does seem to be caused by a JAVA_HOME set inconsistently with the Java in the PATH and used for installation.

C:\Working\tools\jython2.7.0>echo %JAVA_HOME%
C:\Program Files (x86)\Java\jdk1.6.0_34

C:\Working\tools\jython2.7.0>bin\jython
Traceback (most recent call last):
  File "<string>", line 444, in <module>
  File "<string>", line 435, in main
  File "Z:\jythondev\jython27\src\shell\build\jython\out00-PYZ.pyz\subprocess",
line 522, in call
  File "Z:\jythondev\jython27\src\shell\build\jython\out00-PYZ.pyz\subprocess",
line 710, in __init__
  File "Z:\jythondev\jython27\src\shell\build\jython\out00-PYZ.pyz\subprocess",
line 958, in _execute_child
WindowsError: [Error 2] The system cannot find the file specified

C:\Working\tools\jython2.7.0>java -version
java version "1.7.0_65"
Java(TM) SE Runtime Environment (build 1.7.0_65-b19)
Java HotSpot(TM) 64-Bit Server VM (build 24.65-b04, mixed mode)

C:\Working\tools\jython2.7.0>set JAVA_HOME=C:\Program Files\Java\jre7

C:\Working\tools\jython2.7.0>bin\jython
Jython 2.7.0 (default:9987c746f838, Apr 29 2015, 02:25:11)
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java1.7.0_65
Type "help", "copyright", "credits" or "license" for more information.
>>> def fib(n):
...     if n <= 1:
...         return n
...     return fib(n-1)+fib(n-2)
...
>>> fib(5)
5
>>> fib(6)
8
>>> fib(8)
21
>>>
C:\Working\tools\jython2.7.0>