无法创建页面方法“GetCompletionList”，因为找不到CodeBehind或CodeFile文件！ Ajax Visual Studio 2012

I am am in need of help with regards to the following error that I am getting when clicking on "Add AutoComplete page method" on a textbox control in an aspx page: "Cannot create page method "GetCompletionList" because no CodeBehind or CodeFile file was found!". This is related to adding an Ajax control to a webpage object such as a textbox.I am am in need of help with regards to the fol