POP3 Problem

Hi, Since upgrading to 7.1 on my mail server, I am getting the following problem when trying to collect mail from my Windoze clients (I can collect mail locally) "The TCP/IP connection was unexpectedly terminated by the server (Account :'phil' Pop server: 'fred', error number : 0x800ccc0f)" I have no problems with any other network or TCP/IP access to this machine. Cheers Phil