The reasons and solutions for not being able to access the course selection platform of East China University of Science and Technology are as follows:

1. Network congestion: Due to the large number of courses, the platform may not be able to carry too much traffic. You can try visiting during off-peak hours, such as before or after the course starts, or wait for a while before using a faster network environment.

2. Server failure: It may be due to the temporary failure or maintenance of the server, which makes it inaccessible. In this case, you can try again later, or contact the technical support department of the school for help.

3. Browser compatibility: The browser used may be incompatible with the course selection platform, or some settings of the browser may be configured incorrectly. You can try to change your browser or set browser compatibility.

4. Personal network problem: It may be because of poor network environment or network equipment failure, which leads to inaccessible. You can try to change the network environment or check the settings of network devices.

5. Course selection platform system update: the system may be updated or upgraded, resulting in some functions unavailable. This kind of situation can be used after a while, or contact the technical support department of the school to ask about the update.