Recently I have not been able to send or receive emails in my Windows Live Mail program.  I can get the emails in webmail on Yahoo.com and on my mobile devices but not in Windows Live Mail.  The error message that comes in is

Unable to send or receive messages for the Charlotte Chamberlain account. Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity.

Server: 'pop.att.yahoo.com'
Windows Live Mail Error ID: 0x800CCC0F
Protocol: POP3
Port: 995
Secure(SSL): Yes

A friend suggested that I have kept too many emails but deleting batches of them doesn't help.  Any suggestions?