sock_init Hangs when Multicast Used On Network Segment

We’re running a BL4S160 and Dynamic C 10.70. sock_init() works fine until we add a device to that segment of the network that uses multicast. sock_init() then hangs. If I use sock_init_or_exit(1) I get “waiting for interface…” over and over forever. The light on the BL’s port will flash for about a second and then go out every time “waiting for interface…” is output.

We have the BL4S160 hooked into a Hirschmann SPIDER II 8TX switch, which is 10/100. I found the following link when I Googled the problem, but that’s obviously not our problem since this switch is 10/100.

I have tried setting _ETHERNET_INIT_DELAY_MS to different values as specified in a net.lib comment, but it didn’t help.

Any ideas on what would cause this problem and how to fix it?