Put your code in try catch finnlay, and then remember to call cnn. Near Fenray. Or you'll fail in surgery or something, cnn. Close will definitely not be executed, which will cause you to access different SQL in this case. It can only be opened by one user at a time, and others have to wait.
I set up this database in SQLSERVER. After reporting the error, I also thought about this problem. After restarting, SQLSERVER did not open and the service was closed. I ran it directly with VS, and it was still an error.
In addition, the provident fund system will also be upgraded. After upgrading, you can log in and use it normally. If you are not in a hurry to handle business, you can log in again in two days.