File "electrum\gui\qt\network_dialog.py", line 447, in set_server
  File "electrum\network.py", line 547, in set_parameters
  File "electrum\network.py", line 251, in func_wrapper
  File "electrum\network.py", line 563, in switch_lagging_interface
  File "electrum\blockchain.py", line 295, in read_header
  File "electrum\blockchain.py", line 257, in assert_headers_file_available