[CentOS] Hylafax does not pick up.

We run the distro HylaFax on a CentOS-5.4 host. On infrequent occasions we notice that the server will not pick up an incoming call. It reports listening to modem rings.

Now, it seems to me that picking up the call should be under the control of the modem but I notice that there exists a setting in Hylafax for the number of rings before picking up. The default value for this is 0 (zero) but we have it set to 1 (one). Because of this option I am not sure whether there is something wrong with the server or with the modem.

Has anyone else experienced this problem and discovered its cause?