Registering problems

[Pilsward]

I registered the devices we have at the start of the day to work out which ones were totally flat so I could replace the batteries. After replacing the batteries on a number of devices, I cleared the list of registered devices so I could re-register them in order (ours are numbered). However, when I tried to do this, none of the devices would connect, even the ones that didn't have their batteries changed. They all had the lights flashing when I pressed the flame in the centre so I know that the new batteries work. I tried another classroom but had the same problem. I just tried again now and found that they will register and work if you are really close to the light on the board (within 1-2 metres), but will not work if you are further away. Does anyone know what this problem might be?

We have the older Activotes with the flame as the centre button.
We are using Activstudio 3
The boards we have are about 4-5 years old, connect via USB, are using firmware V3.36 and Driver V1.3

Help!

Thanks,

Mark

PS- Our computers are installed with a zero-card which removes any changes once you log out, which is why we have to register the activotes every time we want to use them.