[ASP.NET] If you already have an open DataReader associated with this Command, you must first close it.

The above error occurs when two or multiple sqldatareaders are opened at the same time. Because sqldatareader is used to read database data, sqlconnection is on but not closed.

    I checked online and found that a SqlConnection can only execute a transaction once, and it must be closed and then opened again. I only used it once above and did not turn it off, and it turned on directly, so it will report an error. In fact, you don't have to open it multiple times, so it's very troublesome to implement. Just add MultipleActiveResultSets=true directly after the connection string. If there is a configuration file, you can modify the configuration file directly.