try
string sqlCommand = "INSERT INTO Users (Username,[Password],RegisterEmail) " + "VALUES('" + userName + "','" + passWord + "','" + email + "')";
And use connection string with Provider
string connectionString = @"Provider=Microsoft.Jet.OLEDB.4.0; Data Source=C:\Users\Sagitta\Documents\RS_Studio_Login.mdb";
More information about connection strings :
http://www.connectionstrings.com/access/[
^]