RedGate.SQL.Shared.Utils.ExecuteBlock errors out

System.NullReferenceException: Object reference not set to an instance of an object.
   at RedGate.SQL.Shared.Utils.ᐁ(Object , SqlInfoMessageEventArgs )
   at System.Data.SqlClient.SqlConnection.OnInfoMessage(SqlInfoMessageEventArgs imevent)
   at System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection)
   at System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj)
   at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj)
   at System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async)
   at System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe)
   at System.Data.SqlClient.SqlCommand.ExecuteNonQuery()
   at RedGate.SQL.Shared.Utils.ExecuteBlock(ExecutionBlock block, String server, String database, Boolean integratedSecurity, String userName, String password)
   at RedGate.SQL.Shared.Utils.ExecuteBlock(ExecutionBlock block, String server, String database)
   at Service.CompareAndComplyDatabase(String ServerName, String DatabaseName, String UserName, String Password)

    [WebMethod(Description = "")]
    public void CompareAndComplyDatabase(string ServerName, string DatabaseName, string UserName, string Password) 
    {
        Database db1 = new Database();
        Database db2 = new Database();

        //copy from
        db1.Register(new ConnectionProperties(
               WebConfigurationManager.AppSettings["SQL_ServerName"].ToString(),
               WebConfigurationManager.AppSettings["SQL_DatabaseName"].ToString(), 
               WebConfigurationManager.AppSettings["SQL_UserName"].ToString(), 
               WebConfigurationManager.AppSettings["SQL_Password"].ToString()
            ),
            Options.Default);

        //copy to
        db2.Register(new ConnectionProperties(
            ServerName,
            DatabaseName,
            UserName,
            Password
            ),
            Options.Default);


        Differences differences = db1.CompareWith(db2, Options.Default);

        foreach (Difference d in differences)
        {
            d.Selected = true;
        }

        Work w = new Work();
        w.BuildFromDifferences(differences, Options.Default, true);

        ExecutionBlock b = w.ExecutionBlock;

        Utils u = new Utils();
        u.ExecuteBlock(b, 
            ServerName,
            DatabaseName
            ,
            true,
            UserName,
            Password);

        b.Dispose();
        db1.Dispose();
        db2.Dispose();
    }