I had the same problem when they installed Fios last week. According to the guy, they use HDMI 1.2 cables and the cable i had must not have been up to date, he switched the cable to his and it has worked ever since. I also have a Samsung TV.
I dont know if anyone noticed this, but they have also added SCIFI-HD
(I cant post urls, but lookup up via imdb tv listings)
Since Fios just added USAhd and CNBChd, i'm hoping that they get these channels in time for the olympics