Network activation errors

Okay so not the biggest of deals, but just thought you should know. When using the plugin with WPMU and setting to network activate, adding new blogs throws up errors in the header when the plugin is automatically activated. Turning off network activate, and manually deactivating and activating plugin made the errors disappear. Examples of errors

Fatal error: Cannot unset string offsets in /home/mydirectory/public_html/wp-content/plugins/wordpress-seo/wp-seo.php on line 90

Warning: in_array() [function.in-array]: Wrong datatype for second argument in /home/mydirectory/public_html/wp-content/plugins/wordpress-seo/inc/class-sitemaps.php on line 540

try to save any changes

Warning: in_array() [function.in-array]: Wrong datatype for second argument in /home/mydirectory/public_html/wp-content/plugins/wordpress-seo/inc/class-sitemaps.php on line 540
Warning: Cannot modify header information - headers already sent by (output started at /home/mydirectory/public_html/wp-content/plugins/wordpress-seo/inc/class-sitemaps.php:540) in /home/mydirectory/public_html/wp-includes/pluggable.php on line 934