Error "Cannot have multiple items selected in a DropDownList" after clicking the Setting button on the Admin->Content Type->Page Types-Settings

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We get this error when trying to access page setting from within the Admin area.

Error "Cannot have multiple items selected in a DropDownList" after clicking the Setting button on the Admin->Content Type->Page Types-Settings

Cannot have multiple items selected in a DropDownList.

[HttpException (0x80004005): Cannot have multiple items selected in a DropDownList.]
   System.Web.UI.WebControls.DropDownList.VerifyMultiSelect() +96
   System.Web.UI.WebControls.ListControl.RenderContents(HtmlTextWriter writer) +9719093
   System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.Control.Render(HtmlTextWriter writer) +12
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   ASP.episerver_cms_admin_contenttypeinformation_ascx.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in C:\Code\SVN\trunk\MVC\Mosaic\EPiServer\CMS\Admin\ContentTypeInformation.ascx:14
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +268
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.Control.Render(HtmlTextWriter writer) +12
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   ASP.episerver_cms_admin_editpagetypesettings_aspx.__RenderGeneralSettings(HtmlTextWriter __w, Control parameterContainer) in c:\TempASP.NETFiles\vs\d578a7e3\dc62f13d\App_Web_t5m1fsje.0.cs:0
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +268
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +12
   System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +12
   System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.Control.Render(HtmlTextWriter writer) +12
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.Control.Render(HtmlTextWriter writer) +12
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +106
   System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter output) +53
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +40
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +32
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   ASP.episerver_cms_masterpages_episerverui_master.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in C:\Code\SVN\trunk\MVC\Mosaic\EPiServer\CMS\MasterPages\EPiServerUI.Master:10
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +268
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.Control.Render(HtmlTextWriter writer) +12
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128
   System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13
   System.Web.UI.Page.Render(HtmlTextWriter writer) +29
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100
   System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1303
#178205
May 04, 2017 15:46
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