Take a note of all the add-ons that are on the list when you click 'Start game' then 'Add-ons'.
Go to your add-ons folder and find a certain 'Weapon_Ra' and temporarily drag it onto your desktop, making sure that it is no longer in your add-ons folder.
Then go back to Blockland and start a server, and see which one is missing from the add-on list.
Then, with the add-on still on your desktop, try join that server that crashed again. See what happens.