The xml file stores all addresses that are geocoded, so next time you preview the map, we don't have to geocode, which make it faster to preview the map. The xml file is only generated if you have a server side langauge site such as PHP, ASP, or ColdFusion. If you are you using an HTML site, the xml file is not generated, but you can create an empty xml file and save it in the _promaps_cache folder. This should clear the error that you are receiving in the Safari error counsel.
If you need more help, please submit a support ticket to further assist you.