using System;

using static System.Console;
using System.Globalization;

class DebugFour4
{
static void Main()
{
double sales, commission;
string inputString;
const int LOWSALES = 1000;
const int MEDSALES = 5000;
const int HIGHSALES = 10000;
const double LOWPCT = 0.05;
const double MEDPCT = 0.07;
const int BONUS1 = 1000;
const int BONUS2 = 1500;

WriteLine("What was the sales amount? ");
inputString = ReadLine();
sales = Convert.ToDouble(inputString);

commission = LOWPCT * LOWSALES;

if (sales <= LOWSALES)
commission = LOWPCT * sales;
else if (sales <= MEDSALES)
commission = LOWPCT * LOWSALES + (sales - LOWSALES) * MEDPCT;
else if (sales <= HIGHSALES)
commission = LOWPCT * LOWSALES + (MEDSALES - LOWSALES) * MEDPCT + BONUS1;
else
commission = LOWPCT * LOWSALES + (MEDSALES - LOWSALES) * MEDPCT + BONUS1 + BONUS2;

WriteLine("Sales: {0}\nCommission: {1}",
sales.ToString("C", CultureInfo.GetCultureInfo("en-US")),
commission.ToString("C", CultureInfo.GetCultureInfo("en-US")));
}
}

In the original code, there is a logical error in calculating the commission based on the sales amount. The error lies in the calculation of the commission for sales amounts between MEDSALES and HIGHSALES.

Here is the corrected code:

```csharp
using System;
using static System.Console;
using System.Globalization;

class DebugFour4
{
static void Main()
{
double sales, commission;
string inputString;
const int LOWSALES = 1000;
const int MEDSALES = 5000;
const int HIGHSALES = 10000;
const double LOWPCT = 0.05;
const double MEDPCT = 0.07;
const int BONUS1 = 1000;
const int BONUS2 = 1500;

WriteLine("What was the sales amount? ");
inputString = ReadLine();
sales = Convert.ToDouble(inputString);

if (sales <= LOWSALES)
commission = sales * LOWPCT;
else if (sales <= MEDSALES)
commission = LOWSALES * LOWPCT + (sales - LOWSALES) * MEDPCT;
else if (sales <= HIGHSALES)
commission = LOWSALES * LOWPCT + (MEDSALES - LOWSALES) * MEDPCT + (sales - MEDSALES) * 0.1;
else
commission = LOWSALES * LOWPCT + (MEDSALES - LOWSALES) * MEDPCT + (HIGHSALES - MEDSALES) * 0.1 + BONUS2;

WriteLine("Sales: {0}\nCommission: {1}",
sales.ToString("C", CultureInfo.GetCultureInfo("en-US")),
commission.ToString("C", CultureInfo.GetCultureInfo("en-US")));
}
}
```

This corrected code now correctly calculates the commission based on the sales amount provided by the user.