Windows Authentication for Specific windows user group

I created asp.net webpage , i want to log on my asp page using windows username and password when login button click. i have search some code(http://www.codeproject.com/Articles/37558/Windows-Authentication-Using-Form-Authentication) in net for login my asp page. It works for my local user name and password but i want to access Specific domain group members to my asp.net page

The second Modal in my ASPX file doesn’t Post when clicking submit button

I have an ASPX file that contains two modals (myModal and addModal) and a gridview that has buttons calling each of these. I am having trouble with the second modal when opening and clicking its Submit button as it won’t fire a PostBack. Its only a problem with the second one. If I change the sequence of these Modals within the ASPX file, then I again have trouble only with the second one in the file.