How to lock the sequencer from the driver

I am trying to create a driver with two stage pipeline using the example given on uvm_transaction entry of uvm on-line reference as shown below.

task do_item();
forever begin
mbus_item req;
lock.get();
seq_item_port.get(req); // Completes the sequencer-driver handshake
accept_tr(req);
// request bus, wait for grant, etc.
begin_tr(req);
// execute address phase
// allows next transaction to begin address phase
lock.put();
// execute data phase
// (may trigger custom "data_phase" event here)
end_tr(req);
end
endtask: do_item

when I compiled my version using irun, it complained about

ncvlog: *E,ILLHIN (driver.sv,233|13): illegal location for a hierarchical name (in a package).

Could anyone please tell me what is the right way to lock the sequencer in the driver.

thanks,