With the new forums now live, now's a good time for me to post this thread.
Based off of past experience and giving support to others, this thread's purpose is to offer common fixes for various errors, crashes and startup problems with TrackMania that can be quite common, and a fair amount of people have faced.
This is by no means an exhaustive list; new errors and fixes may pop up in future.
Game launch error messages:
"Corrupted installation. Please verify files or reinstall the game."
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Although the first immediate obvious fix, as indicated, is to either verify files or reinstall the entire game, there may also be some other causes:
Make sure you're running Ubisoft Connect as admin. Otherwise, the game may not have read/write privileges, and cannot access required config files.Make sure your antivirus isn't interfering. Same reason as above.Make sure that your PC meets the minimum system requirements. You might scoff at this, but I've seen reports of people trying to run the game with only a 1GB GPU, or worse, an Intel HD chipset, and they complain about not being able to run the game when the minimum system requirements specify a 2GB GPU.
"File infected! This program has been manipulated and maybe it's infected by a Virus or cracked. This file won't work anymore."
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This error message is actually very misleading, and is the result of the game's VMProtect being unable to initialize.
This error message appears to be very common with players who are specifically using F-Secure antivirus. If you are, and you have this message, you must manually whitelist the game .exe in your antivirus settings.
"To improve performance, it is recommended to free up 5.0GB. Currently you only have X_XGbytes (page_file/commited memory)"

This is not strictly an error message, and you are able to still launch the game when you close it. This message appears when your PC currently has less than the recommended commit size available.
Commit size is a combination of RAM and page file on your system. To free up commit size, you need to either kill programs/processes that are using up a considerable amount of RAM, and/or increase the page file size on your internal hard drive.
"Error at hooking API "LoadStringA". Dumping 32 first bytes:"

This error message is common if for some reason your Visual C++ Redistributables are corrupt, not up to date, or have not been installed.
You can redownload the Visual C++ Redists here (make sure to install both the 32-bit and 64-bit packs).32-bit: https://aka.ms/vs/16/release/vc_redist.x86.exe: (https://aka.ms/vs/16/release/vc_redist.x86.exe)64-bit: https://aka.ms/vs/16/release/vc_redist.x64.exe: (https://aka.ms/vs/16/release/vc_redist.x64.exe)
Common problems found in-game
When joining a server, I appear to stuck in an overview of the map, and cannot do anything.

If your game is stuck in a similar position as the above photo, and pressing Escape does nothing, then bad luck, you got what's known in the community as a "joinbug". This can usually happen if your connection drops while the game is trying to synchronise your client to the server.
While there is currently no "one-size-fits-all" solution, players have reported that playing a map in solo before playing online helps avoid this.Alternatively, there is an OpenPlanet plugin which permits a force rejoin to attempt to get around this bug. OpenPlanet is a dev-authorised extension for TrackMania, allowing for extra addons and scripts to be used.You can download OpenPlanet here: https://openplanet.nl/: (https://openplanet.nl)The joinbug workaround script can be downloaded here: https://openplanet.nl/files/75: (https://openplanet.nl/files/75)
Even on high-end hardware, I appear to be suffering from framerate drops and microstuttering.
Unfortunately, TrackMania is not a very well optimized game, and when there's a lot happening on screen at once, even the best rigs will get FPS drops from time to time.
If you do not have it enabled, attempting to enable CPU/GPU synchronisation in the graphics settings may help. GPU/CPU synchronisation allows the game to pre-render frames ahead of time, which may help with stabilizing framerate, however cranking it up too much may also introduce input lag.The game settings can be accessed by moving your cursor to the top of the screen, and clicking on the cog icon in the top-right."Very High" Shader Quality is currently unoptimized, and may cause lag. It's recommended to lower it a notch or two.
"You are not connected to UPlay" message when the game loads the main menu.

Has your PC recently woken up from standby or hibernate, and you immediately try to launch the game? That's very likely why. For some reason, Ubisoft Connect hates it when a PC wakes up from standby/hibernate.
A quick restart of Ubisoft Connect (plus running as admin) should clear it right up.
When opening the pause menu while connected to a server, my game freezes for a period of time.
For some reason, the game likes to apply downloaded skins, texture mods and custom signs and load them in-game whenever the game is in an unfocused state - such as being Alt-Tabbed, the pause menu being opened, and so on. When this happens, the game freezes so it can load in all the downloaded content. However, depending on your PC, this may take from either several seconds to several minutes, and has unfortunately bowled people over, especially when they're playing Cup Of The Day.
Disabling downloads in the game settings can help this. You can disable downloads in the game settings, under the System tab.To disable all downloads, untick 'Car Skins', 'Map mods', and 'Map Skins'.Make sure to restart your game to apply the changes.
My game takes a long time to load/crashes when I try to open the Map Editor.
The Map Editor can sadly be a bit of a RAM hog, especially when you're working on larger maps, especially if you're using OpenPlanet to create maps with bigger-than-normal boundaries, and especially if you're working with a ton of custom items or blocks.
If you do have a lot of custom blocks/items in your folders, try moving them out. It should help with bringing down RAM usage.
Despite owning Club Access, I cannot access the Club leaderboards for a map/campaign.
You need to join and pin a Club before you can access Club leaderboards.
When attempting to upload a skin, I receive various errors.
Error C-AA-00-03: Make sure that you've exported the skin that you've created instead of simply saving it.Error 0x0000019D: Your skin is too big. Skins must be under 25MB.
Upon loading in to the main menu, the game will get "stuck" at a Club page or profile page, and pressing Escape to try and back out of it will do nothing as the game will immediately return to the page it was just on.
The solution for this: Make sure that any wheels or joysticks that you may have connected are unplugged before starting the game. Even if you don't think you have anything, it doesn't hurt to double check. I assume the reason for this is because the game is treating such devices as XBox/PS4 controllers, and as such, the analog input from the pedals or a joystick is causing it to repeatedly act as a button press to the game.
Official Response Total Play time shows an incorrect playtime - January Update