PageMethod/WebMethod not being executed

Hi,
    PageMethod which supposed to be called/executed when "onChange' of dropdownlist is triggered is Not being executed. I have 3 dropdownlist being created at runtime/dynamically inside a compositecontrol class and loaded (.dll) in a page at runtime. I have added a scriptmanager in the master page and set EnablePageMethods to true, tried placing the webmethod function outside of the compositecontrol and in the page, still webmethod is not being called... Anyone has idea or solution to this problem of mine? Or another approach to retain the selected value of the dropdownlist inside this compositecontrol (.dll) that is being loaded in a page at runtime?
 
ddlProduct.Attributes.Add("onChange", "javascript:StoreDropDown('" + this.ID + "','',this.options[this.selectedIndex].text,'');"); //used this javascript function is being called but not ...