"Invalid Credentials" on Windows 8

"Invalid Credentials" on Windows 8

I have managed to successfully install the Companion on my Windows Vista and my Windows 8 laptops. I have the app on my Android cell and iPad. I can connect from both my cell and iPad to the Vista but not the Windows 8. I get "Your login credentials are invalid. Please correct and try again." I'm very sure I am using the correct username and password. 

I set up the Windows 8 the same way (using the wizard) as the Windows Vista, so I'm not sure why it's not working. I'm guessing it's some kind of preset setting on Windows 8 that is preventing me from accessing that computer. I have reviewed the Credentials Guide and still don't know what's wrong. 

Any suggestions would be appreciated. Thanks!