The usual solution is simply a permalink reset but, in some cases, this may simply be a server error. So far, we've encountered at least one case that has been resolved using other solutions.
Remember to try a permalink reset first, these other solutions are very rare.
Make sure that you went through the eLearnCommerce Migration after you've updated. Just try going on the Settings page within eLearnCommerce. If you're not redirected to the migration page, it's all good.
Make sure that you don't have any other course plugins that use the post type courses. This normally shouldn't break your site but simply display inconclusive data, however, it can happen.
For the next solutions, we recommend having your hosting company, or your server administrator, or your developer check them.
Make sure that you don't have a folder called courses on the same root folder that has an .htaccess in it. That htaccess will most likely be accessed when visiting the courses page.
Make sure that you don't have any strange .htaccess rules that could affect specific course links. Previous customers that have migrated from other solutions forgot to clean up and they've had this issue.