(#4) Application request limit reached

It sometimes happens when the Facebook api is receiving too many calls in a short period of time. There are no official numbers but it seem to happen if there are more than 600 calls per 600 seconds, per token & per IP. The message automatically disappears after a few minutes (I guess after another 600 seconds).

Using a WordPress plugin for caching is probably the best solution. It will limit the number of calls to the Facebook api and will improve performance overal.