File "electrum\gui\qt\history_list.py", line 702, in <lambda>
  File "electrum\gui\qt\main_window.py", line 3292, in dscancel_dialog
  File "electrum\wallet.py", line 1544, in dscancel
  File "electrum\wallet.py", line 209, in get_locktime_for_new_transaction
  File "electrum\blockchain.py", line 490, in is_tip_stale
  File "electrum\blockchain.py", line 486, in header_at_tip
  File "electrum\blockchain.py", line 201, in func_wrapper
  File "electrum\blockchain.py", line 473, in read_header
  File "electrum\blockchain.py", line 435, in assert_headers_file_available