I get the following crash with 0.5.5. If it matters, i also installed the calculcator and shortcut extensions.

The mod Factory Palette (0.5.5) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event factory-palette::Custom event (ID 388)
Key "state" not found in property tree at ROOT
stack traceback:
[C]: in function 'add'
flib/gui.lua:65: in function 'add'
factory-palette/scripts/gui/search.lua:497: in function 'populate_sources'
factory-palette/scripts/gui/search.lua:477: in function 'build'
factory-palette/scripts/gui.lua:25: in function 'fn'
factory-palette/handlers.lua:20: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>
stack traceback:
[C]: in function 'raise_event'
flib/dictionary.lua:335: in function 'handler'
core/lualib/event_handler.lua:47: in function <core/lualib/event_handler.lua:45>

This is surprising to me. According to the error it's coming from when we add checkboxes for source selection, which sets the state parameter in checkbox here: https://lua-api.factorio.com/latest/classes/LuaGuiElement.html#add this has been available since Factorio 2.0. Can you share some more details?

1. What version of Factorio are you on?
2. What other mods do you have installed?
3. Does this happen on an existing save or new ones or both?
4. If it's only on an existing save, would you be comfortable sharing that with me?