When the eZClusterFileHandler returns an eZClusterFileFailure, the method eZUser::getUserCacheByUserId() returns it and so triggers the error

Cannot use object of type {{eZClusterFileFailure}} as array

and dies. The method should handle the eZClusterFileFailure and return something the caller can work with.

PS: It would certainly be more interesting to find and solve the underlying problem, but the Failures will probably still happen now and then.