We notice that MathSciNet describes this paper as Research Paper 60 with a comment "Paper number later changed by the publisher from 60 to 57".
From the journal's point of view, the paper number was always R57. The pdf that can be downloaded from our website has always described the paper as R57. It has not been changed since it was published on 9 September 2004. The date stamp on the file confirms this. We would ask authors to cite the paper as R57.