system halts in when adding a new category slug to widgets

When I add a new category and change the homepage widgets category slug section "
Warning: stripos() expects parameter 1 to be string, object given in /home/public_html/oktaysaral/wp-content/themes/GameNews/gavern/widgets.nsp.php on line 868

Catchable fatal error: Object of class WP_Error could not be converted to string in /home/public_html/oktaysaral/wp-content/themes/GameNews/gavern/widgets.nsp.php on line 869"

and when I add a new post to an existing category the site halts too. What can be the problem?

Please check the permissions for the cache directory inside the theme directory.

Please check the permissions for the cache directory inside the theme directory.

I checked the permisions they are ok. When I write an post under existing category there is no problem.But when I make a new category and write a post and assign it to gk news module problem starts.

I give all the themes directory 777 but nothing changed.But when I cahnge the theme and do thesame things in thesame wordpress setup everything is ok