The VPOP3 Fax Printer Driver obtains address book details using LDAP. So, you must make sure that the VPOP3 LDAP service is enabled, and that the Fax Printer Driver has the correct VPOP3 address, and the same TCP/IP port defined to access the LDAP service as VPOP3 is using.
Both will default to the standard LDAP TCP port of 389, but if you have another LDAP server on the VPOP3 computer (eg the Windows Active Directory service), then you may have moved (or need to move) the VPOP3 LDAP service to another port, and change the Fax Printer Driver configuration accordingly.