Change password error

Hi my router is the D6220 it wasnt listed in the dropdown so I chose what looked closest. Maybe this needs adding to the list ?

Firmware Version
V1.0.0.72_1.0.72

Every time I try and change the password I get the following error:

400 Bad Request

This server does not support the operation requested by your client.

I've done a factory reset and restored my settings file, Ive tried different browsers and operating system combinations ( Windows 10, Mac and Ubuntu) but all with the same results. I tried to contact Netgear but it seems they have no interest even though this looks like a software bug to me!

Be grateful for any help.

thanks,

Lee.