"Null" error message comes up when trying to stream NBCSN

Chrome does not support Flash content. Use IE or Edge if in Windows 10. 

That didn't work either.  Used Edge on another device, used Edge on my personal device....still Null

When trying access NBCSN streaming sports, I am taken through steps where I am asked to select my service provider.  I select ATT U-verse.  I am then asked to type in my e-mail and password for ATT U-verse.  I do that, then the Null error message appears.

The link to your screenshot didn't work for me, but in Windows 10 permission needs to given by website for Flash to run. It's not obvious either. Play around with it and a pop-up should appear asking permission to run Flash.