The emerging problem is that some of the Freeview boxes have firmware which is not fully compliant with the DVB-T (digital terrestrial TV) standard. Specifically, it is the NIT (Network Information Table) which is giving problems.
The NIT is a table of data sent with the digital broadcasts which contains information about the channels available, all the settings the box needs to use to receive and decode them, etc. Up until recently, a single NIT has been sufficient, but with the growth in the number of channels it was decided to adopt a split NIT, where the data is distributed between two different tables. This is in accordance with the official DVB-T standards, but some boxes do not support it properly. The result is that when your local transmitter switches to the split NIT system, next time your box tries to rescan the channels it won't be able to properly interpret the data and you'll end up with a dead box, unable to retune and receive anything.
Unfortunately, there's very little which can be done besides replacing the receiver. I believe some of manufacturers affected might be offering a free discretionary replacement, but I've only skimmed the details.
I'm not familiar with the BT Vision box, but does it also have an antenna input for receiving local digital channels directly off-air? If so, then incompatible firmware could be the problem there too if you local transmitter has just switched to a split NIT.
Just to make things worse, there is another likely compatibility problem looming on the horizon even for those not affected by this. Digital broadcasts are set to change to a slightly different DVB-T mode after the last analog transmissions are closed down in 2012. It seems that some receivers might have firmware compatibility problems with that, too.
