Reason:530-5.5.1 Authentication Required. Cant send Email

Reason:530-5.5.1 Authentication Required. Cant send Email

I tried sending an e-mail and received this error
  Reason:530-5.5.1 Authentication Required.

Any ideas. I looked at Google with the url from the error message, but there was no information on Google.

Sending failed; Reason:530-5.5.1 Authentication Required. Learn more at 530 5.5.1 http://mail.google.com/support/bin/answer.py?answer=14257 20sm3548370wfi.32

Thanks.

Les..