You are right, but I use the plugin not with a fan page. I’m using it with an open group page. Here I used the ID and it worked fine.
After 3 days without working plugin, suddenly it works without any changes by me. So I think there was a problem on Facebook site, not a problem of the plugin.
But nowadays I can’t find the “old” ids. It seem that facebook changed something. The plugin works an d I hope it will still work in the future.
Thanks for your answer.