I have a brand new smartphone and I constantly get an error message of "authentication error". It will work briefly when I enter the password when I am right next to the router, but it won't save it. The router is brand new and directly from Xfinity.
Is this an Xfinity router issue or a Samsung Galaxy S4 issue?
It's a Samsung issue. You can try setting security to just TKIP. (Haven't tried it long enough to see if it's a real solution.) D-Link suggests turning off WMM (Wireless Multimedia Extensions), which works on my Belkin router, but I have no clue how to do it on the xfinity router.