Issue downloading on iPHone 4S from Calibre Server

I have Calibre server set up which I access on my iPhone 4S using Safari. This previously worked fine.

I find recently that I can access the Server, click the [mobi] button and be taken to the next page where I'm prompted to either open the file in OneDrive or Open In... and given a number of options (Kindle etc). However, nothing actually happens past this point; if I select "OneDrive", nothing happens. If I select "Kindle", then Kindle itself opens but the book is not available. GoodReader: again, nothing happens.

Any help appreciated,


P.