I cannot download a purchased ebooki

i have purchased an ebook but cannot download it as the book icon vanishes before i can clic on it. I have both a version for ipad and one for kindle, which is also on my ipad, and the same thing happens. I have contacted the publishers who tested te ibook on their own device and had no problem. Is there something wrong with ipad or could it have to dowith my email? Many thanks for any thought.