I recently received a similar error whilst building a sequencer and because of the top down nature of connect i needed to do a super.connect() to make sure rsp_export is connected otherwise i got the same error.
class slfbrc_fbrc_master_sequencer extends ovm_sequencer #(slfbrc_dm_fbrc_transfer);
//
// OVM transaction interfaces
//
ovm_analysis_export #(slfbrc_dm_fbrc_transfer) item_collected_export;
local tlm_analysis_fifo #(slfbrc_dm_fbrc_transfer) fbrc_fifo;
//
// Fields
//
slfbrc_dm_fbrc_config m_config;
slfbrc_dm_fbrc_transfer transfer;
//
// OVM automation macros for sequencers
//
`ovm_sequencer_utils_begin(slfbrc_fbrc_master_sequencer)
`ovm_field_object ( m_config, OVM_ALL_ON)
`ovm_sequencer_utils_end
//
// Constructor
//
function new (string name = "slfbrc_fbrc_master_sequencer", ovm_component parent);
super.new(name, parent);
`ovm_update_sequence_lib_and_item(slfbrc_dm_fbrc_transfer)
endfunction : new
//build
function void build();
super.build();
item_collected_export = new("item_collected_export", this);
fbrc_fifo = new("fbrc_fifo", this);
endfunction
virtual function void connect();
**<font color=red>super.connect();</font>**
item_collected_export.connect(fbrc_fifo.analysis_export);
endfunction
endclass : slfbrc_fbrc_master_sequencer