Error in sending mails

Hi All,
I am not sure, if i am posting this question in the right forums. Please let me know the forum details if I am wrong.
Below given is the error which i get when i am trying to call a method to send mails.
{"Client found response content type of 'text/html; charset=Windows-1252', but expected 'text/xml'.
\r\nThe request failed with the error message:
\r\n--\r\n<html>\r\n    <head>\r\n        <title>Runtime Error</title>
\r\n        <style>\r\n        \tbody {font-family:\"Verdana\";font-weight:normal;font-size: .7em;color:black;}
\r\n        \tp {font-family:\"Verdana\";font-weight:normal;color:black;margin-top: -5px}
\r\n        \tb {font-family ...