I've gone through the downloading process again and I think I've found out what's going wrong. Basically when you click to download the Quartus II web edition you are diverted to the registration/login page. Once you've done this you are diverted again to a page which show all the versions of Quartus in a drop down menu. V13.0 sp1 is on the list but it's the full subscription version and not the free web edition. The only way I can seem get back to the free version download is to go back to the original link on Frank's page, after registering. Hope that makes sense
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Regards
David