I have succesfully managed to download metadata for some 740 ebooks without a failure.
This is how i do it, I downloaded and added all the english metadata plugins from here.
I then converted what books needed doing to epub format.
I opened edit metadata (doing each individual ebook).
I checked that the Author and Book Tiles were filled in.
I then removed any information in the
(ids) field.
Finaly I conducted a metadata download (without fail I found the metadata i wanted)
I hope this is of help and good luck
