Darren at Tsohost (who is an absolute star) has rectified the problem for me within the last few minutes. I quote his message:
>You had the character ‘w’ in front of the first PHP line in
/home/departuo/public_html/wp-content/plugins/kcite/kcite.php
>Hence the error. I’ve removed this for you, and the site appears to >be OK now.
The same thing is presumably likely to happen to anyone else using Kcite who is updating to the latest version. I have tried to contact the developers, but their site (https://knowledgeblog.org/kcite-plugin) seems to be down.