Warning: implode() in forum section

Hi,
I use module forum & Omega 4 and in forum sites "/forum" and "/forum/discution" me write message

"Warning: implode() [function.implode]: Invalid arguments passed in template_process() (line 2422 of .../includes/theme.inc)."

I think the problem is in template.php on line 579 where some classes are loaded into the variable "$ variables ['classes_array'] 'as a string.

But I do not know how to solve this problem.

Thank you