I've noticed that you can only do that if you're logged into the Workout Manager.
Sometimes, when I have been logged into the old site, that when it asks me to log into the workout manager, that when I put the correct info in, it doesn't recognise it. If I go back to the original site, log out, and log back in, when I go to workout manager, all is well - don't even have to log on (again) there - I'm somehow already logged into that part too.