Solution to 'Could not find the main class, program will exit' while executing runnable file

This error usually happens if there is a conflict in the Java installations. It means there may be more than one installation of Java in your system. Mostly presence of Oracle Jinitiator in C:\Program Files (x86)\Oracle creates this problem.

Perhaps your file associations got messed up. At the command prompt, try running

ftype | find "jarfile"

On my 64-bit Windows 7 computer, that shows

jarfile="C:\Program Files (x86)\Java\jre6\bin\javaw.exe" -jar "%1" %*

You can also change it with ftype:

ftype jarfile="C:\Program Files (x86)\Java\jre6\bin\javaw.exe" -jar "%1" %*

and reboot the system. 

You may also uninstall the Jinitiator which is no longer supported by Oracle as per our knowledge.