Be careful of some Prolific serial cables you can get on eBay UK.
I bought 6 months ago a serial cable (one of those in the greenish transparent plastic) which I intended to use with Amiga Explorer. It _never_ worked properly. It would just truncate data randomly and cut the connection whenever it felt like it.
Bought another cable and that one worked like a charm. If it's the same issue here it might be cutting off the connection during the programming...