I am having the exact same issue. One day it was fine (I watched 2nd Vietnam video) and the next day, when I tried to watch the 3rd it wouldn't load and I got the same message. I also removed the PBS channel and re-loaded it but it didn't work. Odd thing is that I can watch the same videos on a second tv in the house. I called the PBS help line and was prompted to leave my name and number. Of course it's been almost 24 hours and no one has called me back. If anyone finds a fix for this please post. Thanks.
You wrote that you removed the channel then reinstalled it. Note that there's a missing step. It is, in this order, and with no steps omitted:
1. Remove the channel
2. Reboot the Roku
3. Reinstall the channel
Now, that won't always fix things, but it's a first step, as RokuShawnS pointed out earlier. And, the steps must be those steps, not an abbreviation of them. Most people don't do step 2, and that's just as important as the other steps.
Do those, then let us know if the issue remains.