Wanted to first thank you for taking on this project. This is a wonderful plugin and I for one appreciate your time spent on this.
After upgrading to the latest version of both wordpress and league manager I was getting the 'Could not load template' warning for a custom template I had on my home page. Digging deeper into the code to find out what the issue was as I had not changed anything other than upgrading I found the use of TEMPLATEPATH in shortcodes.php. Correct me if I am wrong but I understand that TEMPLATEPATH has been deprecated.
Changing this to get_stylesheet_directory() fixed the issue (especially since I am using a child theme).