Sorting of bibliography by author

Hello, Thanks very much for reviewing my question. I am writing an article to be published in the Foot and Ankle International. They require that the bibliography is sorted by alphabetical order. I am using the AMA style ie numbers for inline citation and Bibliography starting with the Author then title etc. I've been into the visual editor and added SORT to bibliography, selected macro in TYPE and author as Macro to sort. however it does not allow me to SAVE STYLE, each time I try to save I get this message: Error saving the style:undefined Message: invalid style Please help. What should I do to add sort function to the bibliography?