A new version of Sharing Cart for 2.7 has just been released which we believe solves the AJAX problems. Please update to Sharing Cart 2.6 release 1 patch 5.
https://github.com/VERSION2-Inc/moodle-block_sharing_cart
Best regards,
Don Hinkelman, on behalf of...
Tomonori Maruyama, Sharing Cart Programmer
Version2 Web Development