Having changing my mods configuration, CXXL woud not start any more (error message or nothing). Installing my old mods configuration made nothing to it. Having install of CXXL from scratch (without mods of cours), then still STEAM, CXXL did not always want to start . The problem was the prototypesdb.bin file (in C:\Users\UserName\AppData\Local\Focus Home Interactive\Cities XXL\live\data\config). Why? Because this file contains the configuration of your mods. And this configuration can be bad specialy when mods are dependent from each other. What is almost always the case. To understand the problem, it is necessary to understand how the game loads mods and packs. In the starting up the game begins by loading the packs of the game. Then it loads mods. Which allows the mods to overwrite basic packs. Fine. But what appens when a mod B uses an other mod A? We must known that there no dependency tree in XXL. The mods are loaded as they arrive, as they are registred the first time. Usualy the load B is developped long time after the mod A. And then it is loaded after too. Then the reference A verses B is OK because A was registred long time before. But if you deleted the mod A for any reason from the "mods" directory, the game will crash when the mod A is asked at the load of a city using the mod A... or B!. The reflex is to reinstall the mod A. Every one will do it. I do it. But it isn't the good reflex. Why ? Because the mod B will be loaded before the mod A in the prototypesdb.bin. And the reference used by B on A will be a crasy reference. If we are happy, the game crashes at the start. If not, it will crash whenever later. I think it is a main reason of game instability. To remove all mods and then to registre all then is not a trustfull solution. Why? If the prototypesdb file is "corrupted", the game will not start. And if it is not (what is worth), the modes will be loaded independently of their dependence. If we are lucky..... The good practice woud be to remove A and B at the time. And then to registre first A (-> starting the game only with mod A), and then B. If we missed it, the only solution I see is to remove the prototypesdb.bin and then register all mods respecting their dependencies: first independant mods and then dependants.