Error 10055 means that Windows has run out of TCP/IP socket buffers because too many connections are open at once.

Things to check if this happens are:

• Is there any other TCP/IP software running on the same PC as VPOP3 - eg a proxy server
• Use a virus scanner to check for malware, as some malware is badly written and will use a lot of connections
• Use a program such as TCPView or NETSTAT (with the -b parameter) to see which programs have connections open

Current versions of Windows can support many thousands of IP connections at once. Server versions can support more than desktop versions if you have a busy server, so it is unlikely that VPOP3 on its own will deplete the socket buffers, and the problem is usually some other software.