In some versions of VPOP3, occasionally the Status Service may get disabled if there was a problem during initialisation - this will prevent the VPOP3 Status Monitor from connecting to VPOP3.
To check this, run RegEdit, and find HKEY_LOCAL_MACHINE\Software\PaulSmith\VPOP3\Service\Number8 on the left. Then, on the right, check the value of the Enabled setting. If this is set to 0 then the service is disabled.
To re-enable the service, stop VPOP3 (eg by killing it from the Processes list in Task Manager, or by stopping the service), then, in RegEdit, change the value of the Enabled setting to 1 and restart VPOP3