Server Error in '/MSReserv' Application.

Cannot have multiple items selected in a DropDownList.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: Cannot have multiple items selected in a DropDownList.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[HttpException (0x80004005): Cannot have multiple items selected in a DropDownList.]
   System.Web.UI.WebControls.DropDownList.VerifyMultiSelect() +130
   System.Web.UI.WebControls.ListControl.RenderContents(HtmlTextWriter writer) +201
   System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +50
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +132
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +271
   System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +47
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +132
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +271
   System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter writer) +208
   System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter writer) +47
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +132
   System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter writer) +69
   System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +271
   System.Web.UI.Page.Render(HtmlTextWriter writer) +39
   System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +132
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +8680


Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.8.4700.0