populating a dropdown from database using javascript webservice

i wanted to use using database to populated the dropdown but i am getting error as type or list space cannot be found at ListCountry GetCountries as its defined static the web methood code is in the same aspx.cs page how culd i use it if a different webmethod page .asmx is created

ref : http://www.aspsnippets.com/Articles/Populate-Bind-DropDownList-using-JavaScript-and-ASP.Net-AJAX.aspx