Problem with replies

I keep getting 'a fatal error'

Fatal error: Uncaught Error: [] operator not supported for strings in /hermes/walnacweb03/walnacweb03al/b2067/moo.bladestormmx/silent-death/forum/newreply.php:826 Stack trace: #0 {main} thrown in /hermes/walnacweb03/walnacweb03al/b2067/moo.bladestormmx/silent-death/forum/newreply.php on line 826

And the same here. Something has gone very wrong with the host, and we're actively looking for a new host to handle our forum needs...