i would recommend always use the @ sign before path strings to avoid problems like yours: you need 1 more back slash before "visual studio 2010". for example:
@"C:\Users\skysoft\Documents\visual studio 2010\Projects\MailSend\MailSend\CsvFile\"
also, you are giving the method
"C:\\Users\\skysoft\\Documents\visual studio 2010\\Projects\\MailSend\\MailSend\\CsvFile\\" + op1.FileName
which translate to
"C:\\Users\\skysoft\\Documents\visual studio 2010\\Projects\\MailSend\\MailSend\\CsvFile\\" + "c:\\...."
you should do Path.GetFileName(op1.FileName)
as keyboardP said or op1.FileName.Substring(op1.LastIndexOf('\\'))