I've had exactly the same problem; I only downloaded 2.79 today. The previous version was 2.5 or some such.

After getting this error, I tried several things:

- I set up a .bat file to manually set the path to a suitable Java runtime environment, and also set the classpath. No go.

- I tried the "Repair" option from the installer.

- I tried uninstalling the program, then reinstalling.

Still nothing works.