Q: Multiple subqueries, one returns more than 1 row  SELECT NOMBRE_E 'EMPLEADO'
 FROM EMPLEADOS
 WHERE IDEMPLEADO = (
     SELECT IDEMPLEADO FROM ENVIOS WHERE IDPRODUCTO = (
         SELECT B.IDPRODUCTO
         FROM ENVIOS B
         GROUP BY B.IDPRODUCTO
         ORDER BY COUNT(*) DESC
         LIMIT 1
     )
 )


ERROR: Subquery returns more than 1 row

how to fix it?

A: A quick fix is to add another Limit 1. But it is hard to say if it is correct without more information.
SELECT NOMBRE_E 'EMPLEADO'
 FROM EMPLEADOS
 WHERE IDEMPLEADO = (
     SELECT IDEMPLEADO FROM ENVIOS WHERE IDPRODUCTO = (
         SELECT B.IDPRODUCTO
         FROM ENVIOS B
         GROUP BY B.IDPRODUCTO
         ORDER BY COUNT(*) DESC
         LIMIT 1
     )
     LIMIT 1
 )


A: You have two subqueries.
     SELECT B.IDPRODUCTO
     FROM ENVIOS B
     GROUP BY B.IDPRODUCTO
     ORDER BY COUNT(*) DESC
     LIMIT 1

And
 SELECT IDEMPLEADO FROM ENVIOS WHERE IDPRODUCTO = (
     ...
 )

The first has a LIMIT 1 on it to guarantee it only returns one run. The other does not. The simple fix is to add a LIMIT 1.
 SELECT IDEMPLEADO FROM ENVIOS WHERE IDPRODUCTO = (
     ...
 ) LIMIT 1

However, you should first examine why this query is returning more than one row. It appears to be selecting an employee ID from the shipments table based on the product ID. If it returns more than one employee, a LIMIT 1 will pick an employee from that list at random. You probably don't want that.
If it's the case that it's returning the same employee ID multiple times, you can use DISTINCT to reduce it to just 1.
 SELECT DISTINCT IDEMPLEADO FROM ENVIOS WHERE IDPRODUCTO = (
     ...
 )

If it's returning different employee IDs, you have to question whether this is the right query to be running. For example, the first query uses a GROUP BY B.IDPRODUCTO ORDER BY COUNT(*) DESC LIMIT 1 to sort the list by how many times each B.IDPRODUCTO is seen and return the one that's seen the most. That may also be appropriate for your other subquery.

A: SELECT NOMBRE_E 'EMPLEADO' 
FROM EMPLEADOS 
WHERE IDEMPLEADO = (SELECT DISTINCT(IDEMPLEADO) 
                    FROM ENVIOS 
                    WHERE IDPRODUCTO = (SELECT B.IDPRODUCTO 
                                        FROM ENVIOS B 
                                        GROUP BY B.IDPRODUCTO ORDER BY COUNT(*) DESC LIMIT 1) );

In the outer subquery, maybe a distinct or MAX if it's numeric. Hope this helps.

A: I believe you can resolve this by using an IN or Exists clause instead of using an equals. This will allow the subquery to return multiple results 
SELECT NOMBRE_E 'EMPLEADO'
FROM EMPLEADOS
where exists
(
        SELECT IDEMPLEADO
        FROM ENVIOS
        WHERE IDPRODUCTO = (
                SELECT B.IDPRODUCTO
                FROM ENVIOS B
                GROUP BY B.IDPRODUCTO
                ORDER BY COUNT(*) DESC LIMIT 1
                )
                and ENVIOS.IDEMPLEADO = Empleados.IDEMPLEADO
        );

or an IN clause 
SELECT NOMBRE_E 'EMPLEADO'
FROM EMPLEADOS
WHERE IDEMPLEADO in (
        SELECT IDEMPLEADO
        FROM ENVIOS
        WHERE IDPRODUCTO = (
                SELECT B.IDPRODUCTO
                FROM ENVIOS B
                GROUP BY B.IDPRODUCTO
                ORDER BY COUNT(*) DESC LIMIT 1
                )
        )


A: Your first subquery is returning more than 1 row.
WHERE IDEMPLEADO = (
   SELECT IDEMPLEADO FROM ENVIOS WHERE IDPRODUCTO = (

You can use 'IN' instead of '='
WHERE IDEMPLEADO IN (
     SELECT IDEMPLEADO FROM ENVIOS WHERE IDPRODUCTO = (

However, it's better you check why you're getting multiple values (1-n), whether you want to use all or select limit 1 or maybe you have a new problem now:)
