Hey,
We're running a WPMU setup with the Sitewide Feed Plugin and on our global feed we get this error message:
Warning: Invalid argument supplied for foreach() in E:\xampp\htdocs\wpmu\wp-content\plugins\gd-star-rating\gd-star-rating.php on line 1915
Warning: Invalid argument supplied for foreach() in E:\xampp\htdocs\wpmu\wp-content\plugins\gd-star-rating\gd-star-rating.php on line 1915
I think I tracked it down to line 1111 in gd-star-rating.php. Usually this line would not get executed for feeds but unfortunately the sitewide feed plugin does not change the is_feed value in wp_query and therefore is_feed() still returns false in this case...
Obviously it would be the job of the sitewide feed plugin to make sure its feeds are actually recognised as feeds, but maybe you could also make sure that your variables are arrays before you use them in a foreach loop!? :-)