It seems that there are several common issues that can cause problems when importing an .atlas file. Here are some steps you can take to troubleshoot and resolve the issue:

1. Check for BOM (Byte Order Mark): Ensure that your .atlas file is saved without a BOM. You can use a text editor like Notepad++ to check and remove the BOM if present.

2. Verify File Extensions: Make sure that the file extensions are correct. For example, the .atlas file should not have an incorrect extension like .atlas.tx.

3. Check for Missing Regions: Open the .atlas file in a text editor and ensure that all referenced regions are present and correctly named. Missing or incorrectly named regions can cause import failures.

4. Ensure Associated Files are Present: Make sure that the associated .png files are present and correctly referenced in the .atlas file. Sometimes, the issue can be due to missing or incorrectly named image files.

5. Re-export the Atlas: If the atlas is not up to date with the skeleton file, try re-exporting it from Spine to ensure consistency.

6. Check for Transparency Issues: If you are using a texture packer, ensure that the setting "Ignore blank images" is disabled, as it might exclude necessary regions from the atlas.

7. Provide Complete Files: If the issue persists, provide the complete set of files including the .skel, .atlas, and associated .png files for further investigation.

Here is a summary of the steps you can take to troubleshoot the issue:

• Ensure the .atlas file is saved without a BOM.
• Verify that file extensions are correct.
• Check for missing or incorrectly named regions in the .atlas file.
• Ensure all associated .png files are present and correctly referenced.
• Re-export the atlas if it is not up to date with the skeleton file.
• Disable "Ignore blank images" in the texture packer settings if necessary.
• Provide the complete set of files for further investigation if the issue persists.

If you follow these steps and still encounter issues, please provide the complete set of files including the .skel, .atlas, and associated .png files for further assistance.

@jmpastorfide As the error message in the screenshot reads, you're trying to import a 3.6 .json file in Spine Editor version 4.2. You need to change the Editor version to the same version of the .json file first, then import, then you can save it as a Spine project. It's always best to keep the original Spine project files around and not depend on re-importing exported files.