1. Data input error: There may be errors when entering class information, such as spelling mistakes and wrong class code. In this case, you can recheck whether the entered course information is correct.
2. Data synchronization delay: It may be that the class information in the system is not updated in time, which makes it impossible to query the class temporarily. This may be caused by system maintenance or network delay. In this case, you can wait for a while and then query again.
3. Category does not exist: the category may not exist in the system. This may be because the system has set permissions and can only query some classes. Or the class is not included in the student health monitoring system. In this case, it is recommended to contact relevant departments or administrators for inquiry and solution.
If the above reasons are not applicable, it is recommended to further communicate with the system administrator or relevant person in charge to understand the specific situation and seek solutions.