A big change has happened to how broadcast TV channels work in the UK, and loads of people have no idea.
For years and years, loads of channels in the UK have been broadcast in two versions - an old-school 'standard definition' or SD version, and a newer HD version that looks way better.
Plenty of set-top boxes now default to the HD versions since they're an improvement in every way, but until recently you did have the option of watching either - no matter how you connected.
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In early January, though, the BBC turned off its SD channels by satellite, so that you can now only watch the HD versions over the air. The SD versions are still available through Freeview, though - they're only being canned over satellite.
If you're stuck on a really old TV with no recent set-top box, you might now be finding that when you try to watch SD versions of BBC One or BBC Two, you're getting a 'Channel closed' message or some other error that arrives when the channel itself doesn't show up.
Well, sadly there's not much you can do about this, unless you upgrade your hardware to a TV and/or Freeview box that supports HD content (which will certainly be anything launched in the last few years).
You can call the HD Satellite Upgrade helpline to get guidance and a clear explanation of everything - but it closes this week.
The number you can call is 0330 123 1876, and you better do so before 5pm on 16 February, because that's the point when the line will stop being used and you won't be able to access support anymore.
From the BBC's point of view, this will doubtless free up a lot of resources that it's been dedicating to the ever-shrinking pool of people still watching in SD quality, but one can imagine that some of those people are less than pleased right now.
In practice, this will be a welcome upgrade once you commit to it, of course - the difference between the flaky SD satellite experience and the easy convenience of HD through an affordable Freeview box is pretty stark.
However, it's also not free, no matter how you look at it, so there will be people who feel this wasn't a necessary change and they're being forced to pay to upgrade when they were perfectly happy before.