SqlCommand is returning an error when attempting to execute a query using c#

I am working on a project that will allow the users to build a query just by selecting columns.

My application seems to be working fine and generating the correct queries. But when I execute the query I get the following exception

Column 'Tasks.Duration' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

What does not make since here is that my query actually includes the correct GROUP BY statement

Here is the query that my application generated

SELECT
 [Campaign].[Title] AS [CampaignTitle]
,CASE WHEN [Task].[Duration] <= @p0 THEN @p1 WHEN [Task].[Duration] >= @p2 AND [Task].[Duration] <= @p3 THEN @p4 ELSE @p5 END AS [9pl1WbY1ZkSvSpel3g4xmw]
,COUNT(1) AS [Ib7ZS4arHkSUWhf4saEtmg]
,SUM(CASE WHEN [Task].[Duration] <= @p6 THEN @p7 ELSE @p8 END) AS [xW1GmttC6kWHsc9QIEPN9w]
FROM [Tasks] AS [Task]
INNER JOIN [Campaigns] AS [Campaign] ON [Campaign].[Id] = [Task].[CampaignId]
INNER JOIN [Users] AS [User] ON [User].[Id] = [Task].[CompletedBy]
INNER JOIN [Results] AS [Result] ON [Result].[Id] = [Task].[ResultId]
WHERE
[Result].[IsCompleted] = @p9 AND ( [User].[LastName] = @p10 OR [User].[LastName] = @p11 )
GROUP BY
[Campaign].[Title]
,CASE WHEN [Task].[Duration] <= @p13 THEN @p14 WHEN [Task].[Duration] >= @p15 AND [Task].[Duration] <= @p16 THEN @p17 ELSE @p18 END
HAVING
COUNT(1) >= @p12
ORDER BY
 [Campaign].[Title]
,CASE WHEN [Task].[Duration] <= @p19 THEN @p20 WHEN [Task].[Duration] >= @p21 AND [Task].[Duration] <= @p22 THEN @p23 ELSE @p24 END

Better yet, I tried to manually replace the parameter names with parameter value. Then I took they output query and I executed it in SSMS and it worked with no problems.

This is how I execute the query

using (SqlConnection connection = new SqlConnection(this.connectionString))
using (SqlDataAdapter sqlAdapter = new SqlDataAdapter(selectCommand))
{
    try
    {
        selectCommand.Connection = connection;

        DataTable table = new DataTable();

        sqlAdapter.Fill(table);

        return table;
    }
    catch (Exception e)
    {
        throw new ReportException(string.Format("{0} {1}", e.Message, e.GetType().FullName));
    }
}

Here is the method that I used to replace the parameters with their values

private string GetPlainQuery(SqlCommand selectCommand)
{
    string output = selectCommand.CommandText;

    for (int i = selectCommand.Parameters.Count - 1; i >= 0; i--)
    {
        var p = selectCommand.Parameters[i];

        string value = p.Value.ToString();

        if (p.SqlDbType == SqlDbType.NChar || p.SqlDbType == SqlDbType.NText || p.SqlDbType == SqlDbType.NVarChar || p.SqlDbType == SqlDbType.Text || p.SqlDbType == SqlDbType.Char || p.SqlDbType == SqlDbType.Date || p.SqlDbType == SqlDbType.DateTime || p.SqlDbType == SqlDbType.SmallDateTime)
        {
            value = string.Format("'{0}'", value.Replace("'", "''"));
        }

        output = output.Replace(p.ParameterName, value);
    }

    return output;
}

What is causing this error? How can I fix it?

UPDATED

Here is the query after I replaced the parameters with the values

SELECT
 [Campaign].[Title] AS [CampaignTitle]
,CASE WHEN [Task].[Duration] <= 100 THEN '<100' WHEN [Task].[Duration] >= 100 AND [Task].[Duration] <= 200 THEN 'BETWEEN 100 AND 200' ELSE '>200' END AS [9pl1WbY1ZkSvSpel3g4xmw]
,COUNT(1) AS [Ib7ZS4arHkSUWhf4saEtmg]
,SUM(CASE WHEN [Task].[Duration] <= 100 THEN 1 ELSE 0 END) AS [xW1GmttC6kWHsc9QIEPN9w]
FROM [Tasks] AS [Task]
INNER JOIN [Campaigns] AS [Campaign] ON [Campaign].[Id] = [Task].[CampaignId]
INNER JOIN [Users] AS [User] ON [User].[Id] = [Task].[CompletedBy]
INNER JOIN [Results] AS [Result] ON [Result].[Id] = [Task].[ResultId]
WHERE
[Result].[IsCompleted] = 1 AND ( [User].[LastName] = 'Yo' OR [User].[LastName] = 'Smith' )
GROUP BY
 [Campaign].[Title]
,CASE WHEN [Task].[Duration] <= 100 THEN '<100' WHEN [Task].[Duration] >= 100 AND [Task].[Duration] <= 200 THEN 'BETWEEN 100 AND 200' ELSE '>200' END
HAVING
COUNT(1) >= 0
ORDER BY
 [Campaign].[Title]
,CASE WHEN [Task].[Duration] <= 100 THEN '<100' WHEN [Task].[Duration] >= 100 AND [Task].[Duration] <= 200 THEN 'BETWEEN 100 AND 200' ELSE '>200' END