Network connection problem or system failure or maintenance. If you encounter the problem that you can't submit your paper to the library of Nanjing University of Technology because of network connection, please make sure that your network connection is normal, and try to reload the page or submit it using other networks. The library system will fail or maintain, which will lead to the failure to submit the paper. You can try to submit it again later, or contact the technical support department of the library for help.