Hi guys
I'm sooo sorry, I just re-re-re checked my ebooks and discover that 2 of them (which were the main problem) where tagged as epub2 but were intended to be epub 3 ... so mostly my fault
I corrected that and now this 2 ebooks pass the epub validator successfully ... but still, according to Smashword standard, not sure they make it to their premium store as some epub3 tricks are not welcome on their website (not criticising them here, they are doing a great job ... just sharing info).
Thanks everyone, I learned a lot in the process.
Happy Christmas !