We tried to download a file at the specified address, but got a permission error. If this is a S3 URL, you probably need to grant read access to Zencoder for this bucket or file. The easiest way to do this is to use a S3 client, like Amazon's AWS Console.
In technical speak, this means that we got a 403 Access Denied response from the server.
Make sure that permissions on the file at the given URL allow Zencoder access. If the file is on S3 you may need to grant read access to Zencoder.