I am trying to convert a string to a datetime format in C#. 

```
DateTime SnapDate = Convert.ToDateTime(valid(odr, 4)).Date;

protected string valid(OleDbDataReader myreader, int stval)//if any columns are found null then they are replaced by zero
{
   object val = myreader[stval];
   if (val != DBNull.Value)
      return val.ToString();
   else
   return Convert.ToString("");
}

```

And it gives me the following error: "The string was not recognized as a valid DateTime. There is a unknown word starting at index 0."

I tried several things like: `parse` and `parseExact` but still didn't get it.

I am reading this data from an excel sheet.