DS-2CD2655FWD-IZS unable to upgrade firmware from v5.5.51 to any later versions

Hi

I have 7 x DS-2CD2655FWD-IZS cameras and they are all running firmware v5.5.51 and they won't upgrade to a later firmware.

The error message displayed from the camera web interface is: failed to get the upgrading progress

Please could anyone suggest how we can apply later firmware ?

We have tried a full reset from the web interface and actually using the camera reset button but nothing helps

Thanks in advance