live555 组播失败 failed to join group异常

live555 组播失败 failed to join group错误
在做live555服务器时。组播模式。new Groupsocket()后老是有如下错误：
22:37:34 Groupsock(5: 232.196.74.220, 18888, 255): failed to join group: setsockopt(IP_ADD_MEMBERSHIP) error: unknown error
22:37:34 Groupsock(6: 232.196.74.220, 18889, 255): failed to join group: setsockopt(IP_ADD_MEMBERSHIP) error: unknown error

哪位高手指导一下？



[解决办法]
组播地址不对？