p-660hwp-d1 router not accepting firmware update

Having had this brand new router sat on my shelf for about 5 years thought it was time to use it, unfortunately the homeplug side won't connect to my existing hp-av network consisting of two TP-link hp-av units and one zyxel pla-4321.
No problem i thought the tplink units did the same but were fine after a firmware update, but no matter what i try i cannot get the router to update it's firmware.
Tried the downloads from both zyxel de and .com ftp sites (no mention of this model on the uk site) and the only non generic error message i can get is when i upload via tftp
this was bought in uk from biggest PC retailer and has a BT compatible sticker on it and works fine with dsl and wireless.
for some reason it thinks the firmware uploaded is for a different model but after triple checking label/existing firmware vs  download ids it is not.
No method will accept the firmware with its existing 340APD2C0.bin filename (causes a -11 write error)but renaming it to ras prior to tftp transfer gives the following error
Any ideas?



#CPE_May