Getting Exception while trying to retrieve images from Flickr

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C#

C#4.0

Have a nice day to all...
I am trying to retrieve User Images from flickr to My C# Mvc Application ..for getting Images from Flickr..so that i created an App register with Flickr. I had my API & Secret
..now this is my code for user to enter his credentials and redirects to My application

public ActionResult Flickrcall()
{
           f = new FlickrNet.Flickr(API, SECRET);
           url = f.AuthCalcWebUrl(AuthLevel.Write);
}

and after redirecting another get call will makes by the flickr as per which i registered to call..Here is the get method..which is getting exception..

[HttpGet]
public ActionResult Flickr()
    {

    try
    {
        oUser = (User)Session["oLoggedInUser"];
        MyLibraryViewModel model = new MyLibraryViewModel
        {
            ImageUrlList = new List<string>(),
            UserLibraryDetails = new List<UserLibrary>()
        };
        if (oUser != null)
        {
            f = new Flickr(API, SECRET);
            string frob = f.AuthGetFrob();
            OAuthRequestToken or = new OAuthRequestToken();
            url = f.AuthCalcWebUrl(AuthLevel.Write);
            or = f.OAuthGetRequestToken(url);
            f.OAuthAccessToken = or.Token;
            f.OAuthAccessTokenSecret = or.TokenSecret;
            Auth auth = f.AuthGetToken(frob);-->Invalid FROB(exception)
            f.AuthToken = auth.Token;
            FoundUser user = auth.User;
            FoundUser userInfo = f.PeopleFindByEmail(UserId/UserEmail);
            :
            :
            :
        }
  }
  catch(Exception Ex)
  {
   string mes=ex.message;
  }
}//End of Method

all the thing what i am doing is ..i need to get UserId or UserEmail..so that I can pass them to the method

f.PeopleFindByEmail(UserId/UserEmail);

..
I am very Happy if i get any Suggestion/Advice's..towards right way..
1-->i have Api & Secret
2-->i calculated for Url
3-->i get Request token and Token secret
4-->I an trying to get FROB()--->Exception (Invalid Frob)
5-->Get OAuth Token from FROB
6-->assigning UserID/UserEmail to Identify User in flickr-->I struck here to get UserId