Breath of the Wild is an extremely complex game, and as such a number of things can potentially go wrong when installing and merging mods, or even just setting up BCML. This page catalogues the most common problems when using BCML and what you can do about them.

Though BCML's installer does not offer a desktop shortcut, it does create a Start Menu shortcut. Open your Start Menu and search for BCML to launch it.

This usually means that Python has not been correctly added to your PATH. You can solve that here:

https://lmgtfy.com/?q=add+python+to+path

You have set your Cemu directory in the BCML settings incorrectly. The exact folder you put into BCML must be the one that contains Cemu.exe and settings.xml.

This usually indicates either that your game dump and/or Cemu directory is set incorrectly, or it could mean that your update data or DLC data is not installed in the correct location for Cemu. The exact location of each folder will be determined by the Cemu MLC folder and by the title ID of your game. BCML supports both the old Cemu MLC layout (pre-1.15.11c) and the new one (1.15.11c+). The exact pattern BCML uses is hard to summarize, but here's an example:

If BCML is searching for TitleBG.pack, and you have the North American version of BOTW, it will check the following locations in order (though, obviously, the search through DLC files will be irrelevant for TitleBG.pack):

1. Update data (new MLC): MLC_FOLDER/usr/title/0005000E/101C9400/content/Pack/TitleBG.pack
2. Update data (old MLC): MLC_FOLDER/usr/title/00050000/101C9400/content/Pack/TitleBG.pack
3. Base game: GAME_DUMP_FOLDER/Pack/TitleBG.pack
4. For the DLC (new MLC): MLC_FOLDER/usr/title/0005000C/101C9400/content/0010/Pack/TitleBG.pack
5. For the DLC (old MLC): MLC_FOLDER/usr/title/00050000/101C9400/aoc/content/0010/Pack/TitleBG.pack

In order to find your game's title ID, BCML will go up one folder from game dump directory (e.g. from BOTW/content to BOTW/) and then check code/app.xml.

For more information on how BCML locates game content, see the source code for util.py, especially the sections starting here and here.

This one is as it says. BCML didn't find a rules.txt file in the mod you picked. BCML only supports either graphic pack mods or BNPs. Other formats will need to be converted first.

The mod you are trying to install contains a BYML file (often ActorInfo.product.sbyml) that has been corrupted by an outdated BYML tool.

If the full text of the error includes anything about XML, you probably either (1) have an old version of Cemu or (2) have a corrupt Cemu settings file. Make sure you have at least Cemu 1.15, and if you still have issues, try deleting settings.xml from the Cemu folder.

The cause of this bug is unknown, and reinstalling Cemu is the only known fix.

Check if the rest of the error text says anything about subprocess or wszst_yaz0. If so, your problem is probably that you are running 32 bit Python, but BCML requires 64 bit Python.

Any time you have any problem with one or more mods in-game after installing them through BCML, the first thing you should try is using the Remerge button.

This indicates a problem with a bootup file, generally either Bootup.pack itself, a file within it, or one of the Bootup_XXxx.pack message packs containing game texts. First thing to try is to Remerge. If that doesn't solve it, it could be a problem with any mod that affects game texts or Bootup.pack, so you can try investigating those.

This is usually a problem of mod priority. Try setting the Linkle mod to a higher priority than other mods that affect TitleBG.pack or armours. If you have already done so, try using Remerge. If it still doesn't work, it could be a more complicated problem with your mod configuration; consider clearing your mods and starting fresh.