In ArcGIS, the GetLegendGraphic wms request requires the parameter 'STYLE' as opposed to 'STYLES'. See the 'Parameters of a WMS GetLegendGraphic Request' section on this page. So the proper request would be: http://myserver/services/test/mapserver/WMSServer?TRANSPARENT=true&Layer=mylayer&FORMAT=image%2Fpng&VERSION=1.1.1&SERVICE=WMS&REQUEST=GetLegendGraphic&STYLE=multiple_rules&EXCEPTIONS=application%2Fvnd.ogc.se_inimage&SLD=http://myserver/sld/634352095454800696.xml Given the length of time since this post, I doubt I will be able to help the OP. However, considering there are a couple thousand views from people investigating the same question, and I personally ran into it while investigating this feature, I thought I'd share. Hope it helps someone.
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