Why does a regular forms app close oledb connection but service will not

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C#

Win2008-R2

I have a service I wrote that uses a filewatcher. On create it takes the excel file and truncates table and import it.
It works on my Windows 7 box. When I drag a new file into the folder it imports it. If i drag a newer file it deletes the old data and imports the new data.
On Windows 2012 Server the service works on the first import. on the second drop of a excel file (second time the service tries to import) I get

Error during import of file 20151106.xls
Exception occured in Microsoft JET Database Engine
Exception: The Microsoft Jet database engine cannot open the file. It is already opened exclusively by another user, or you need permission to view its data.

This shouldn't happen as I close the connections

private void copy_excel(string FullPath)
       {

           //Excel command
           string cmdText = "SELECT [ID], [NAME], [PRODID], [FTDATE]"
              " FROM [DAILY$]";

           //Excel connection string
           string excelConnString = "provider=microsoft.jet.oledb.4.0;" +
               " Data Source=" + FullPath + " ;Extended Properties=" +
               "\"Excel 8.0;IMEX=1;TypeGuessRows=0;ImportMixedTypes=Text\"";

//OleDb Command using cmdText and Connection to read Excel
            using (OleDbConnection oleDbConn = new OleDbConnection(excelConnString))
            {
                using (OleDbCommand oleDbCmd = new OleDbCommand(cmdText, oleDbConn))
                {
                    //open excel
                    oleDbConn.Open();
                    using (OleDbDataReader dr = oleDbCmd.ExecuteReader())
                    {
                        DataTable dt = new DataTable();

                        dt.Load(dr); //Load the excel we want to write to Oracle
                        //bulkCopyOracle(dt); commented out for debug 

                    }
                }
            }
      }

The service works fine on my windows 7 box and works for the first file on Windows 2012 server. Why is the service leaving the connection oleDbConn open on Windows Enterprise Server 2012? ?