这个错误可能是由于API请求返回失败引起的。我们可以尝试重新发送API请求并检查响应状态来解决这个问题。以下是C#代码示例：

try
{
    var manifest = derivativesApi.GetManifest(urn);
    // Process the manifest
}
catch (ApiException ex)
{
    if (ex.ErrorCode == 400)
    {
        // Bad Request - invalid URN or non-translated file
    }
    else if (ex.ErrorCode == 401)
    {
        // Unauthorized - token expired or wrong scope
    }
    else if (ex.ErrorCode == 404)
    {
        // Not Found - URN not translated yet or invalid model 
    }
    else if (ex.ErrorCode == 409)
    {
        // Conflict - translation already in progress
    }
    else
    {
        // Other errors
    }
}