Warning messages wen trying to upgrade to 4.1

When I try to upgrade WordPress I receive the following messages. It will not allow me to upgrade. I am not aware of any problems in the site functionality. Thanks for your help.

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in /home/content/d/i/s/distinctivedog/html/wp-content/plugins/woocommerce-mailchimp/classes/class-ss-wc-integration-mailchimp.php on line 172

Warning: Cannot modify header information – headers already sent by (output started at /home/content/d/i/s/distinctivedog/html/wp-content/plugins/woocommerce-mailchimp/classes/class-ss-wc-integration-mailchimp.php:172) in /home/content/d/i/s/distinctivedog/html/wp-includes/pluggable.php on line 1179