By john 
Checkpoint files are the heart of Stable Diffusion. They contain the trained model data that determines the style and quality of generated images. When Stable Diffusion fails to load a checkpoint file, you cannot generate anything until the issue is resolved.
Here is what usually goes wrong and how to fix it.
Why Checkpoint Files Fail to Load
File corruption during download is the most common cause. Checkpoint files are large, often several gigabytes. If the download was interrupted or the file was not fully transferred, the checkpoint LISBOA77 will be incomplete and unreadable.
Incorrect file placement is another frequent issue. Stable Diffusion looks for checkpoint files in a specific directory. If the file is placed in the wrong folder, the software will not detect it.
Incompatible checkpoint formats can cause loading errors. Some checkpoints are saved in SafeTensors format while others use the older .ckpt format. Your version of Stable Diffusion may not support both formats, or may require specific settings to handle one over the other.
Insufficient system memory can also prevent large checkpoints from loading. Some high-quality models exceed 6GB, and loading them requires adequate RAM in addition to GPU VRAM.
Steps to Get Your Checkpoint Working
Verify the file size against the expected size listed on the download page. If your file is significantly smaller than expected, the download was incomplete. Delete it and download again using a download manager that supports resume.
Place the checkpoint file in the correct directory. For the Automatic1111 WebUI, this is typically the models/Stable-diffusion folder inside your installation directory. For ComfyUI, it is usually models/checkpoints.
Check the file extension. If the checkpoint is a .safetensors file, make sure your Stable Diffusion installation is up to date and supports SafeTensors. Older versions may only work with .ckpt files.
Restart the WebUI after placing the checkpoint. The software scans for models at startup, so new files added after launch may not appear until you restart.
Deeper Troubleshooting
If the checkpoint appears in the model dropdown but fails to load, check the console output for error messages. These messages often specify exactly what went wrong, such as missing keys, shape mismatches, or memory allocation failures.
Try loading a different checkpoint to confirm the software itself is working. If other models load fine, the problem is specific to the one checkpoint file.
Verify the integrity of the file using a checksum if one is provided by the model creator. Compare the hash of your downloaded file against the published hash to confirm the file is intact.
If memory is the issue, close other applications to free up RAM and try loading the checkpoint again. Some large models need 16GB or more of system RAM to load properly.
Safety Precautions
Download checkpoints only from trusted repositories like Civitai or Hugging Face. Checkpoint files in the .ckpt format can contain embedded code that executes when loaded. SafeTensors format is safer because it does not support code execution.
Always scan downloaded files with antivirus software before using them, especially .ckpt files from unfamiliar sources.
Summary
Stable Diffusion not loading a checkpoint file is usually a download, placement, or format issue. Verifying the file integrity, placing it in the correct folder, and ensuring your software supports the file format will resolve most problems.