The mod Module Inserter Extended (7.3.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event ModuleInserterEx::on_gui_click (ID 1)
ModuleInserterEx/scripts/import-export.lua:152: attempt to concatenate local 'x' (a nil value)
stack traceback:
ModuleInserterEx/scripts/import-export.lua:152: in function 'check'
ModuleInserterEx/scripts/import-export.lua:26: in function <ModuleInserterEx/scripts/import-export.lua:23>
(...tail calls...)
ModuleInserterEx/scripts/import-export.lua:60: in function <ModuleInserterEx/scripts/import-export.lua:56>
(...tail calls...)
ModuleInserterEx/scripts/import-export.lua:26: in function <ModuleInserterEx/scripts/import-export.lua:23>
(...tail calls...)
ModuleInserterEx/scripts/import-export.lua:60: in function <ModuleInserterEx/scripts/import-export.lua:56>
(...tail calls...)
ModuleInserterEx/scripts/import-export.lua:26: in function <ModuleInserterEx/scripts/import-export.lua:23>
(...tail calls...)
ModuleInserterEx/scripts/import-export.lua:26: in function <ModuleInserterEx/scripts/import-export.lua:23>
(...tail calls...)
ModuleInserterEx/scripts/import-export.lua:60: in function 'check_array'
ModuleInserterEx/scripts/import-export.lua:172: in function 'import_config'
ModuleInserterEx/scripts/gui.lua:1856: in function 'handler'
ModuleInserterEx/control.lua:487: in function 'wrapper'
flib/gui.lua:147: in function 'handler'
flib/gui.lua:177: in function <flib/gui.lua:160>

Oops, forgot to update the import process for the 7.3.0 changes.

Fixed in the latest update. You should be able to import strings exported from either the current or older versions.

Thanks