How do I make two sites share one Security database

Hi 
I created two sites, now I want to two sites share the same Security database.  
I created the database on the first site, and on the second site _AppStart.cshtml
set as below
WebSecurity.InitializeDatabaseConnection("connectionString", "UserProfile", "UserId", "Email", autoCreateTables: false); Make it point to the first site, but the second site can not be started. Anyone know how can I solve this issue? ...