This error normally means that you have entered an invalid address on the IP Address to Bind To entries on the Services page in the VPOP3 settings.

The addresses entered here should be either <Any> or the IP address of a LAN adapter in the PC running VPOP3.

Alternatively, this can be caused by timing issues related to a DNS lookup. On the Diagnostics tab in VPOP3, press the TCP/IP Tuning Options button and tick Use Synchronous DNS