Well, I've managed to move code to VS 2012 by creating new solution with same structure and adding code files with some tweaking for system.reflection related code. It works fine now.
However, it seems there is a bug related to thread credential, as it shows null after every call to tweetinvi API, i'm not sure whats the root cause. However, i've added null check for thread credential and set it to application credential if true.
var loggedUser = await UserAsync.GetLoggedUser();
var tweetLists = await TweetListAsync.GetUserLists(loggedUser, true);
// thread credentials show null after returning from the above call (not sure why) Anyway, set it to application credentials and next call succeed
if (TwitterCredentials.Credentials == null)
TwitterCredentials.Credentials = TwitterCredentials.ApplicationCredentials;
var friends = await loggedUser.GetFriendsAsync();
I haven't started investigating authentication module yet, but will update this thread if found root cause. Thanks