microsoft/semantic-kernel · error · NotSupportedException

FileReferenceContent cannot be converted to…

Error message

FileReferenceContent cannot be converted to ResponseContentPart. Only FileReferenceContent with a file id is supported.

What it means

The FileReferenceContent overload of ToResponseContentPart needs content.FileId to build an input-file part referencing an uploaded file. If FileId is null, it throws NotSupportedException.

Solutions

1. Upload the file via the files API first and assign the returned id to FileReferenceContent.FileId.
2. Check the upload result for a non-null id before constructing the content.
3. Handle upload failures explicitly instead of continuing with an empty FileReferenceContent.

Example fix

// before
var fileRef = new FileReferenceContent();
message.Items.Add(fileRef);
// after
var upload = await client.UploadFileAsync(filePath, "assistants");
var fileRef = new FileReferenceContent { FileId = upload.Value.Id };
message.Items.Add(fileRef);

if (string.IsNullOrEmpty(fileReferenceContent.FileId))
    throw new ArgumentException("FileReferenceContent must have a FileId.");

static bool HasFileId(FileReferenceContent c) => !string.IsNullOrEmpty(c.FileId);

try { var part = fileRef.ToResponseContentPart(); }
catch (NotSupportedException ex) when (ex.Message.Contains("FileReferenceContent cannot be converted")) {
    // upload the file first, then assign the returned id
}

When it happens

Trigger: Adding FileReferenceContent to a message before/without a file upload returning an id.

Common situations: File upload failed silently so FileId was never set; constructing FileReferenceContent manually without an id.

Related errors

• AudioContent cannot be converted to ResponseContentPart…
• ImageContent cannot be converted to ResponseContentPart…
• Invalid OpenAI client type
• The agent thread is not a ChatHistoryAgentThread.
• Unsupported content type

AI-assisted analysis of microsoft/semantic-kernel@6da62d372a (2026-08-13). Data as JSON: /api/errors/0e9c89faa2fe3b67. Report an issue: GitHub.

Appendix: source

Thrown at dotnet/src/Agents/OpenAI/Extensions/KernelContentExtensions.cs:57

            var dataUri = new Uri($"data:{content.MimeType};base64,{Convert.ToBase64String(content.Data.Value.ToArray())}");
            return ResponseContentPart.CreateInputImagePart(dataUri);
        }

        throw new NotSupportedException("ImageContent cannot be converted to ResponseContentPart. Only ImageContent with a uri or binary data is supported.");
    }

    internal static ResponseContentPart ToResponseContentPart(this BinaryContent content)
    {
        return content.Data is not null
            ? ResponseContentPart.CreateInputFilePart(new BinaryData(content.Data), content.MimeType, Guid.NewGuid().ToString())
            : throw new NotSupportedException("AudioContent cannot be converted to ResponseContentPart. Only AudioContent with binary data is supported.");
    }

    internal static ResponseContentPart ToResponseContentPart(this FileReferenceContent content)
    {
        return content.FileId is not null
            ? ResponseContentPart.CreateInputFilePart(content.FileId)
            : throw new NotSupportedException("FileReferenceContent cannot be converted to ResponseContentPart. Only FileReferenceContent with a file id is supported.");
    }
}

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