Category required when I do not have anything to pass.

AjaxControlToolkit.CascadingDropDown missing required Category property value for cddMonth.
Parameter name: Category
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.ArgumentException: AjaxControlToolkit.CascadingDropDown missing required Category property value for cddMonth.
Parameter name: Category
i don't have anything to pass as a category.
[WebMethod(Description = "Populate a month list.")]
[System.Web.Script.Services ...