In reply to smukerji:
In the set command you have also to use a string as the simple name:
function void build_phase(uvm_phase phase);
super.build_phase(phase);
uvm_config_db#(int)::set(this, "*", "error_source", ERROR_FROM_SEQUENCE);
endfunction
This presumes ERROR_FROM_SEQUENCE is the value you want to put to the config_db.