Asp Net Membership 4.0 to 4.5.2

I'm trying to upgrading my website from 4.0 to 4.5.2.  I created a new user account with ASP.Net Membership in 4.5.2 and everything works fine.  I can now login correctly, but I have a whole lot of users who created their accounts under the old asp.net 4.0 framework which no longer works (can't login) when the website trys to fetch the information it's null.

Though I try to loginto my old website under asp.net framework 4.0 with my newly created asp.net 4.5 user account and it doesn't work.  I use the same connection string in both websites to access the same database.

I just found the user I created in my database, it created a new table in AspNetUsers in asp.net 4.5 the old user accounts table was aspnet_users in asp.net 4.0

1) so how do I migrate my users from aspnet_users to --> aspnetusers

2) So when I migrate to my aspnet 4.5 website how do the old users in aspnet_users login when it login from aspnetusers table, how do the old users from 4.0 login to 4.5

I get the following error

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error: 


Line 29: 
Line 30:         string username = lbButton.Text;
Line 31:         if (Membership.GetUser(username).IsApproved == true)
Line 32:         {
Line 33:              Session["LoggedIn"] = lbButton.Text.Trim();