SQL connection string for microsoft access 2010 .accdb
See the question and my original answer on StackOverflowFor Acces databases (.mdb, .accdb, etc...), you want to use OleDbConnection, not SqlConnection (SQL Server), like this:
conn = new System.Data.OleDb.OleDbConnection(@"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\BC207\test.accdb")