Windows Live Mail– unable to send mail.

 Several weeks ago I tried to send and receive email in WLM and was unable to do so.  I use Time Warner Cable , Road runner and I contacted them.  They told me I needed to change my server settings to  POP3 110 SMTP 587 .  After some trials and about 40 minutes with them, I started to receive email and thought everything was o.k.  .  Then I tried to send something and received "Server Error 501 Server response 501.5.5.2 Mail From Syntax error Server mail .twc.com  Windows Live Mail error ID:0X800CCC78.  After several more hours(nearly 2 hrs.) with 2 other  TWC people, they determined that it wasn't their problem as the  web mail (roadrunner ) was sending and receiving just fine.  I have even tried installing a different mail program and still cannot send --but receive mail just fine.  The TWC people told me that SMTP 501 error translates into "appears when interscan messaging Security Suite is not working"  I have no idea what that is about.  I've tried several of the ideas talked about here on the community, the last being "repairing all Windows Live programs.  Nothing seems to fix the problem.   Any ideas would surely be appreciated.  I'm using Windows 7 Professional (2011) 64 bit . 
thanks in advance,
Mike A.