smtplib data error

[yazzoo]

Does anyone know what causes an SMTPLIB DataError?

The only thing I can find in the manual is
exception SMTPDataError
     The SMTP server refused to accept the message data.

My problem is a previously functioning script suddenly failed last week. 
  My ISP thinks it maybe something to do with upgrading CPanel on their 
server -- maybe a library was missed, but when I try and execute a 
script I get...

Traceback (most recent call last): File "test-py.cgi", line 790, in ? 
sendemail(EmailFrom, EmailTo, emsg) File "test-py.cgi", line 20, in 
sendemail failed = server.sendmail(EmailFrom, EmailTo, emsg) File 
"/usr/lib/python2.2/smtplib.py", line 685, in sendmail raise 
SMTPDataError(code, resp) smtplib.SMTPDataError: (550, 'Administrative 
prohibition')

Thanks for any suggestions.

Lester.