Hi HCL team and Spencer

I suddenly get an error message in my chat monitor that reads:

Warning: mysql_fetch_row(): supplied argument is not a valid MySQL result resource in /class/database.php on line 262

I can logon to the live chat backend, can browse through all the menus and System configuration but when opening the chat monitor I get this error message right underneath the header (where the browsing users are usually shown.) No changes to hosting or database. Database access seems to be possible since I can get everywhere else.

It points to the while loop in database.php: while ($current_row = mysql_fetch_row($this->result))

Do you have a heads up for me? What could cause this suddenly to show up?
Thanks for your help!