I found a solution to this problem on this page. It seems to be a problem with how the newer versions of WordPress test for cookie support. There’s several examples of code to fix the problem in the comments. The code I used was from Cam on the second page. To make it work for the plugin I just modified the “add_action()” parameters to be “add_action( ‘init’, ‘set_wp_test_cookie’);” and then pasted it in plugin.php right above the rest of the functions on about line 107.
function set_wp_test_cookie() {
setcookie(TEST_COOKIE, 'WP Cookie check', 0, COOKIEPATH, COOKIE_DOMAIN);
if ( SITECOOKIEPATH != COOKIEPATH )
setcookie(TEST_COOKIE, 'WP Cookie check', 0, SITECOOKIEPATH, COOKIE_DOMAIN);
}
add_action( 'init', 'set_wp_test_cookie');