Errors may occur when uploading files, which are indicated by the message ‘Invalid file’. This can usually have two causes:

1.) Unknown file extension or MIME type

Since version 8.1, a system-wide check of upload files has been carried out. This applies to files in the backend as well as in forms. 

This check ensures that a file extension (e.g. .pdf for PDF documents) matches the actual file content. In most cases, no manual adjustment is required. However, certain special file formats may not be recognised correctly.

If this is the case, you can change the configuration in the area:

System settings → General → Custom MIME type mappings -> Notes regarding the content type check of uploads:

You have the following options here:

• Deactivate the check completely.
• Explicitly allow unknown file types.
• Create a custom MIME type mapping (see example in the screenshot).

2.) File contains malicious code or is recognised as a virus

If the file contains malicious code or is categorised as potentially dangerous, the virus scanner intervenes and blocks the upload.

If you are sure that the file does not contain malware/viruses (e.g. after a local scan with antivirus software), you can temporarily deactivate the virus scanner via the system plugins:

1. Temporarily switch off the virus scanner.
2. Upload file.
3. Activate the virus scanner again immediately.

⚠ Important: Always check whether the uploaded file actually corresponds to the expected version in order to avoid security risks.