string line = null;
string line_to_delete = "the line i want to delete";
using (StreamReader reader = new StreamReader("C:input")) {
using (StreamWriter writer = new StreamWriter("C:output")) {
while ((line = reader.ReadLine()) != null) {
if (String.Compare(line, line_to_delete) == 0)
continue;
writer.WriteLine(line);
}
}
}