Microsoft.Office.Interop.Excel.Application excel = new Microsoft.Office.Interop.Excel.Application();
Microsoft.Office.Interop.Excel.Worksheet sheet;
Microsoft.Office.Interop.Excel.Range rng;
 
 
System.Runtime.InteropServices.Marshal.ReleaseComObject(rng);
rng = null;
 
System.Runtime.InteropServices.Marshal.ReleaseComObject(sheet); 
sheet = null;
 
 
wBook.Close(true, xlsFile, true);
System.Runtime.InteropServices.Marshal.ReleaseComObject(wBook);
wBook = null;
excel.Quit();
 
System.Runtime.InteropServices.Marshal.ReleaseComObject(excel);
excel = null;
 
GC.Collect(); //на всякий случай