I am posting this for both mods and not sure if this is something that can be resolved (or resolved easily).

I downloaded a bunch of mods at one time to go through and test out that include Advanced Tanks and Tankwerkz Ltd. On game relaunch I got an error message when loading prototypes as follows:

Error while loading item prototype "flame-tank"
(item-with-entity-data): Prototype "flame-tank" registered twice
Modifications: tankwerkz

Clicking the OK button closes the game.

Deleting either one of these mods resolves the conflict.

That is because this mod was created from someone playing with Tankwertz and then making their own mod. It's not an error, it's just that both mods add Flame tanks. You'll either need to modify the code in one of the mods so that it doesn't have the flame tank, or choose only one mod.