Yep, that is one long title for this post.
I had a need to uninstall a Cisco VPN client from Windows 8.1. Attempting to do so resulted in a failed uninstall and two error boxes. First showed Internal error 2503 then was Internal Error 2502.
I did the usual, made sure time and date were correct, I knew I was an admin user, proper permissions were set for admins on the program folder.
The workaround is this: Open task Manager and find Windows Explorer and end task on it. This will terminate your desktop and task bar etc. DON’T PANIC!!
Next go to the top menu and click File then select Run New Task.
Type Explorer.exe in the input box. Make sure to check the box run with administrator privileges if there is a check box, otherwise the message will tell you it will run with administrator privileges. This will restart the desktop shell.
Proceed to uninstall or install and it should work normally.