Hi Bruce,
FYI: I upgraded to the latest version of your Google Sitemap and I noticed some files were not loading with this error so I had to turn off the Property Agent.GoogleSiteMapProvider.
An Exception has occured : Method not found: 'System.Collections.Generic.List`1<Ventrian.PropertyAgent.PropertyInfo> Ventrian.PropertyAgent.PropertyController.List(Int32, Int32, Ventrian.PropertyAgent.SearchStatusType, Int32, Boolean, Ventrian.PropertyAgent.SortByType, Int32, Ventrian.PropertyAgent.SortDirectionType, System.String, System.String, Int32, Int32, Int32 ByRef, Boolean, Boolean)'. - trace: at iFinity.DNN.Modules.GoogleSiteMap.PropertyAgentGoogleSiteMapProvider.GetPropertyAgentPropertyPages(PortalAliasInfo alias, TabInfo tab, ModuleInfo module, ModuleDefinitionInfo modDef) at iFinity.DNN.Modules.GoogleSiteMap.PropertyAgentGoogleSiteMapProvider.GetPropertyAgentSitePages(PortalAliasInfo portalAlias, TabInfo tab) at iFinity.DNN.Modules.GoogleSiteMap.PropertyAgentGoogleSiteMapProvider.SitePagesForTab(PortalAliasInfo portalAlias, TabInfo tab) at iFinity.DNN.Modules.GoogleSiteMap.GoogleSiteMapProvider.GetModuleSpecificPages(PortalAliasInfo portalAlias, TabInfo ti, Locale locale, GoogleSiteMapProviderCollection providers, Int32 sitemapNum, Int32 urlCount, Int32 startingCount, Int32 endingCount) at iFinity.DNN.Modules.GoogleSiteMap.GoogleSiteMapProvider.GetSitePages(Int32 sitemapNum, Int32 startingIndex, Int32 endingIndex) at iFinity.DNN.Modules.GoogleSiteMap.GoogleSiteMapProvider.WriteSitemapPages(XmlTextWriter writer, Int32 sitemapNum)