Sudden error message

When creating new posts this morning, I’m met with the message :

Warning: preg_match(): Unknown modifier ‘k’ in /home/PRIVATE/public_html/wp-content/plugins/bluet-keywords-tooltip-generator/functions.php on line 128

(URL edited for privacy)

I’ve checked the code and can see no errors, there’s not been any updates.
What’s going on ?
Many thanks

• This topic was modified 8 years, 2 months ago by energiseltd.