function in javascript included file is not working

hi,
I am using mixed validation i.e. dot net controls validation and javascript validation. Javascript(js) function is 'hpVali()'. It is working when coding javascript within aspx page's head section. but when i moved it in a js file. It stoped working.
I have used the script to register/add js file in aspx.cs file as:
protected void Page_Load(object sender, EventArgs e)
        {

            string jsName = "ButtonClickScript";
            string jsUrl = "~/Script/regVali.js";
            Type jsType = this.GetType();

            ClientScriptManager cs = Page.ClientScript;

          &n ...