I got this error message upon loading my save game. In my save, I have built a bulldozer and it's standing somewhere on the ground. I'm on Factorio 0.13.9 and Bulldozer version 1.2.6.

http://imgur.com/PXigdvS

Me too, got it on my server

Le Mod bulldozer n'est plus compatible avec la version 0.13.9. On est obligé de désinstaller lors du lancement du jeu. mais on peut le récupérer la partie une fois lancée.
On remet le Mod puis on fait à nouveau la recherche Du Bull. Le seul soucis c'est qu'il ne faut plus quitter Factorio sinon on est obligé de recommencé la procédure.
J'espère qu'il y a aura un moyen de parer à ce problème car le bull est vraiment trop utile pour la déforestation et créer les lignes de chemin de fer pour le train.

What Koukloff is saying (in English) is that its not compatible with the newest release. You can fix it by first removing the mod, reloading the world, saving, then re-installing the mod and doing the research again. You must do this every time you quit out and re-launch the game. (enough for me to stop using the mod unfortunately)

Shame, it's a useful mod, hopefully it will be updated

Please, please, please ckhawks- will you fix this bug? The problem (for me at least) is that the bulldozer was left in the "collect" condition, and Factorio didn't like us saving and/or leaving the game while it was "on". If I knew how to fix this, I would submit that for you, but I have very limited knowledge of programming. :(

Getting this too:
Error while running event on_tick (ID 0)
bulldozer/control.lua:34: attempt to call method 'collect' (a nil value)

you need to delete it every time you shutdown the game, and reload it in the mod folder.

You'r able to unlock it again after this, in the research again.

Error while running event on_tick (ID 0)
bulldozer/control.lua:34: attempt to call method 'collect' (a nil value)

I now have to restart my game thanks to this... Three days total playtime wasted and I now have to start over

Hey all... there is a fixed version of this mod: https://mods.factorio.com/mods/amwdrizz/bulldozer-fixed/
If anyone else has this bug just replace the bulldozer mod with this and when you load your save it will work - and you get to keep your dozer and the research. I'm posting this here so that anyone who encounters this in the future can keep their save.