It probably starts to fall over when you add programmes to a watchlist - meaning that when you log on to the site, it will tell you when your programmes are scheduled to be broadcast.
Other problems I've found - it doesn't show "Last of the Summer Wine" in my watchlist, until Dec 27th (although it is on every day) and my radio programmes aren't showing either, but it does list them in catch up (iPlayer)
I suspect it is like much that happens with online offerings these days! Look at this website for instance, the old one worked perfectly well but they upgraded to this new version and there have been many problems with it since launch.
It just goes to show that newer does not necessarily mean better!
Here's another error message I keep getting over the last few days:-
500 - Internal server error.
There is a problem with the resource you are looking for, and it cannot be displayed."
Using a link to my programme list on the old site, it would take 2 seconds to display them all for the next 2 weeks. The new site, IF it works, takes about 40 seconds minimum & often more. The old site has more of my programmes set up to be listed than the new one, so it shows how fast it was.