3.9.7 happily running here with no installation issues.

Thank you all. Clearly something iffy with my setup. I rolled back to 3.9.6_BT as I still had a copy and know that works, and then moved straight to 3.9.7_BT and all seems to be working fine...

I have tried several times to upgrade and it fails every time. I had upgraded to 3.9.7_STD from the Draytek.com site by mistake. After speaking to Draytek Support today just before they closed they recommended upgrading to 3.9.7_BT from draytek.co.uk. I have not been able to do this and I keep getting the alarming message that my router will die after the next reboot which is disconcerting? Does anybody have any advice please?

As above, downgrade... then upgrade. worked for me...

Unfortunately I do not have the 3.9.6 previous version of the firmware

I went to the downloads on draytek.co.uk to find the old 396 and did the upgrade which worked and then went back to do the 397 upgrade and it failed again.