I don't think updating to 5.1 is the issue.
I am still on 4.4.4 and I am having the same problem today.
Everything was fine a few days ago.
I am no expert, but I am thinking ice films will have to release an add on up date for the apple tv before it starts working again. I know that when the new sources first came out about a month ago, it was awhile before they worked with apple tv because an ice films update had to be sent out.
If anyone has a working apple tv with ice films right now please post so we know.