Cannot access admin area but site is still running

I run a site and recently there were some plugins updated and since the update the wp-admin receives this error:
Warning: Illegal offset type in /home/content/15/8808515/html/clothing1/wp-includes/plugin.php on line 69

Warning: Cannot modify header information – headers already sent by (output started at /home/content/15/8808515/html/clothing1/wp-includes/plugin.php:69) in /home/content/15/8808515/html/clothing1/wp-includes/pluggable.php on line 866

Therefore the wp-admin area cannot be accessed. I have searched for this specific error but with no luck. Can someone please help me with this error?