Hi, Thanks for the prompt responses guys, I think I've cracked it!
I'd already tried reinstalling from TTHome and copying the Loquendo folder across to the SD but nothing, also tried copying the voices folder but still no Kate, she shows on the screens and you can select her but no sound whatsoever from the computer voices. Had 8 hours sleep, pondered your responses and tried a different method ... I connected to TTHome and deleted ALL voices using the 'manage your GO' option, rebooted without SD and then a second time with it inserted. Next I went into the device files and deleted the residual Vocaliser folder and anything left in the Voice folder, I also removed everything from Loquendo except bin & lib folders and licencecode.txt then I went into the SD Card and made sure there were no Voice/Loquendo/Vocaliser folders and rebooted again for good measure. I was now left with a very sparse Loquendo folder and an empty voice folder on the device. I then reinstalled Kate and Jane voices using TTHome, rebooted and checked to see they were working fine on NC8.351 but still no Kate on 8.398. Finally I Copied the now populated Loquendo and the voice folders across to the SD, rebooted and ......... Kate is there in all her glory!
I think there must have been some junk left over from a previous update/deletion and clearing out the Loquendo and Voice folders has done the trick.