ASP.Net page cannot connect(?) but vs.net for web Server Explorer works

Hi, im trying to fix up a asp.net page that i have taken over.
Im not sure if this is a sql-problem, or asp.net problem, so im trying here.
The SQL-server is locally placed on the same machine as vs.net for web is.
The project uses a Data Connection setup in vs.net 2013, and its icon shows green and i can browse the tables in there.
But when i start the debug with IE as browser, then after a while i get an exception thrown:
System.Data.Entity.Core.ProviderIncompatibleException was unhandled _HResult=-2146233087 _message=An error occurred while getting provider information from the database. This can be caused by Entity Framework using an incorrect connection string. Check the inner exceptions for details and ensure that the connection string is correct. HResult=-2146233087 IsTransient=false Message=An error occurred while getting provider information from the database. This can be caused by Entity Framework ...