Exchange Server POP3 errors

I have Small Business Server 4.5 with the POP3 connector set up to retrieve mail from multiple POP accounts over an ISDN connection. Sometimes it works fine. Other times I get a pair of errors for each user.

Event ID: 12050
POP3. Failed to checkthe POP3 acount for username at host company.com on port 110. The error is 10060(or sometimes 10061).

Event ID: 12052
POP3. An error occurred during a POP3 transaction to host . For username. The error is 10060(or sometimes 10061).

Does anyone know specifically what these errors mean or how to eliminate them? Is there a list somewhere by event ID or error number?