How to solve error of "column already belong to datatable"?

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C#

C#4.0

hey friends,

i am trying to import multiple csv files from a folder using textfieldparser . each csv file contains header and 1 record , but when my import method runs it gives error of "a column named "PTNAME" is already belongs to datatable". i couldnt find the way where to change code . plz help me .

here is my import method,

public void ImportAllFilesOfFolder()
{
try
{
DataTable dt = new DataTable();
string sourceDir = txtsend.Text;
var Icsv = Directory.EnumerateFiles(sourceDir, "*.csv");

foreach (string currentfile in Icsv)
{
using (TextFieldParser parser = new TextFieldParser(currentfile))
{
parser.TextFieldType = FieldType.Delimited;
parser.Delimiters = new string[] { "," };
parser.HasFieldsEnclosedInQuotes = true;

string[] columns = parser.ReadFields();

for (int i = 0; i < columns.Length; i++)
{
dt.Columns.Add(columns[i], typeof(string));
}

while (!parser.EndOfData)
{
string[] fields = parser.ReadFields();
DataRow newrow = dt.NewRow();

for (int i = 0; i < fields.Length; i++)
{
newrow[i] = fields[i];
}

dt.Rows.Add(newrow);
}
}
}
con.Open();
SqlBulkCopy bc = new SqlBulkCopy(con.ConnectionString, SqlBulkCopyOptions.TableLock);
bc.DestinationTableName = "SaiRamH";
bc.BatchSize = dt.Rows.Count;
bc.WriteToServer(dt);
bc.Close();
}
catch (SystemException e) { MessageBox.Show(e.Message); }
finally { con.Close(); }
}

and here is my file structure,

PTNAME,REGNO/ID,BLOOD GRP,WARD NAME,DOC NAME,XRAY,PATHO,MEDICATION,BLOOD GIVEN
Mrs.BHAGWAT SUGHANDA RAGHUNTH,SH1401/00457,,GENERAL WARD (FEMALE),SHELKE SAMEER,MRI LS SPINE-PID L3-4 L5S1 MRI BRAIN --- NAD,BSL (R), IV DICLOGESIC RR DRIP 1-0-1 TAB FLEXURA D 1-0-1 TAB ARCOPAN D 1-0-1 TAB BIO D3 STRONG 0-1-0 TAB ALPRAX 0.5 MG 0-0-1 XYNOSURE GEL L/A 1-1-1 TAB NERVSHINE ER 75 0-1-0 CERVICAL TRACTION AND LUMBAR TRACT ALTER WITH IFT 1-0-1,NOT GIVEN.