[Mono-dev] Cannot load Mono.Security.dll

[APS]

Hi, I've a problem on sending mail with SSL auth.
When sending mail I obtain

Cannot load Mono.Security.dll ---> System.Web.Mail.SmtpException: 
Cannot load Mono.Security.dll
  at System.Web.Mail.SmtpClient.ChangeToSSLSocket () [0x00000]
  at System.Web.Mail.SmtpClient.StartSend 
(System.Web.Mail.MailMessageWrapper msg) [0x00000]
  at System.Web.Mail.SmtpClient.Send 
(System.Web.Mail.MailMessageWrapper msg) [0x00000]
  at System.Web.Mail.SmtpMail.Send (System.Web.Mail.MailMessage 
message) [0x00000] --- End of inner exception stack trace ---

I checked that mono.security.dll is present on the machine both on 
1.0 and 2.0 directories.
I'm missing something?