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This error usually occurs when you attempt to execute the next query before having fully read all the results from the previous queries when using MySQLi to execute multiple queries.

This typically occurs when you use the mysqli_multi_query() function to execute multiple queries without having used the mysqli_free_result() function to release the query results.

Here are some possible causes of this error and corresponding solutions:

1. You are attempting to execute multiple queries simultaneously: if you use the `mysqli_multiQuery()` function to execute multiple queries, you must use the `mysqli_storeResult()` function to store the results in memory and then use the `mysqli_freeResult()` function to release the results before proceeding to the next query. For example:

   $query = "SELECT * FROM table1; SELECT * FROM table2;";
   if (mysqli_multi_query($conn, $query)) {
       do {
           if ($result = mysqli_store_result($conn)) {
               while ($row = mysqli_fetch_row($result)) {
                   // 处理结果
               }
               mysqli_free_result($result);
           }
       } while (mysqli_next_result($conn));
   }

   Please note that when executing multiple queries, you need to use the mysqli_next_result() function to switch to the next result set.
2. You are attempting to use multiple `mysqli::query()` functions simultaneously: This error may occur if you execute multiple `mysqli::query()` calls without using the `mysqli::free_result()` function to release the results. Please ensure that you release the results of the previous query before executing the next query; for example:

   $result1 = mysqli_query($conn, "SELECT * FROM table1");
   // 处理结果集 $result1
   mysqli_free_result($result1);
   
   $result2 = mysqli_query($conn, "SELECT * FROM table2");
   // 处理结果集 $result2
   mysqli_free_result($result2);

If you have tried the above solutions but the issue persists, please check your MySQLi code to ensure that you have properly released all query results. If the problem still persists, try adding an appropriate delay between queries and consider optimizing the queries to reduce query execution time.