Using jQuery Autocomplete in Master Page ASP.Net

Refer:

Using jQuery Autocomplete Plugin for TextBox inside Master Page in ASP.Net

I have checked the above link answer once again. Its working in all the content pages. Also i have kept the TextBox in master page. Please check your PageName where you have assigned the Url.

url: 'Default.aspx/GetAutoCompleteData',

Your Content page name will replace Default.aspx.

Check your parameter name in jQuery Ajax and WebMethod

data: "{ 'username': '" + request.term + "'}",

 Both should be equal.

public static List<string> GetAutoCompleteData(string username)