This error i am getting in uvm_backdoor access

Error: (vsim-3978) test.sv(59): Illegal assignment to class mtiUvm.uvm_pkg::uvm_sequencer_base from class work.top1/wdt_env

Time: 0 ns Iteration: 0 Instance: /top1 File: C:/Users/Administrator/Desktop/hjkhg/top1.sv

** Error: (vsim-8754) test.sv(59): Actual input arg. of type ‘class work.top1/wdt_env’ for formal ‘sequencer’ of ‘start’ is not compatible with the formal’s type ‘class mtiUvm.uvm_pkg::uvm_sequencer_base’.

In reply to SRIMAN:

This looks like you are trying to execute a sequence on a sequencer which is not compatible.
Could you please show the definition of your sequencer and the corresponding sequence?.