In many games, multiplayer is one of the game modes which is more affected by random effects: connection drops, casual errors, players power outages on their PCs and so on …
Sometimes it happens the game gets a desynchronization, and the multiplayer seems lost forever. During gameplay one of the two players gets casually random errors or kicked out of the match. Obviously the game gets unplayable and it seems you have lost the last game save.
To me, it even happened that my game went “quicker” while my friend was the host. Clearly this created problems because, as soon as I hit the attack button, its game was still making computations for the other factions. Randomly, before the match started, one of the two got kicked out of the Steam servers.
The error message was “The Host has left the match” or “Synchronization error”.

In order to solve the problem, both PCs must have the same game save file. Sometimes when the host is saving (or simply during autosave), once the host has saved the file, he shall send it also to the other player connected on the net. However suppose the other player lost connection temporarily or had problems exactly during that time window. He shall never receive the updated save file. Moreover, the two PCs shall have different save game files. And that’s where random errors start flourishing.

Both players try verifying Game Cache for Napoleon Total War.
Right click on the game in the library / Properties/ Local Files and click on “Verify Integrity of Game Files”
I link you here the procedure in Steam valid for all games.

https://support.steampowered.com/kb_article.php?s=3234bcd3a34a3f9c1f0dfc4c3342a9d9&ref=2037-QEUH-3335

If the problem still persists, then continue reading and follow the next step.

It is very simple: both PCs need to have the same game save file. The host PCs has to send its game save file to the other player, which shall put the file in its own multiplayer saves folder. And that’s it ! Nothing more simple.

Even if you installed the game on another drive, different from where the Operating System resides, the files you shall need are located in the Operating System drive.
Suppose then you have installed Windows on the ” C: ” drive, the path to the saves shall be
“C:\Users\YOUR_USER_NAME\AppData\Roaming\The Creative Assembly\Napoleon “
There you shall find the folder
“ save_games_multiplayer “
And guess what? Inside there are all the multiplayer game saves you and your friend made!


It will be sufficient to take the Multiplayer Campaign save file you want to “correct” from the host PC and send it over to the other player, who shall put it inside the same folder on its PC.

That’s because you did not put the tick on the “Hidden items” option in the Windows Explorer. It is located in the “View” tab at the top.

We solved using this procedure. We did not test the reverse procedure (namely the PLAYER PC sending its file to the HOST PC). We do not know if that choice shall solve the problem... If someone shall solve, let us know in the comments.
Thank you for the patience of reading up to here. I hope you shall solve the problem as we did.
I apologize If I made some mistakes but I am not English so it may be I have written some typos, you shall pardon me if it is the case 😉
If you solved I kindly ask you to rate this guide in order to make it more visible, so that other players shall solve their problems too. Thank you !