I use SanDisk which have U3 system as purchased. It could be the problem but I know little about it.
The printers are a charity group which own a far from new machine which they use for printing parish magazines, fliers etc. using handicapped people for feeding, folding and stapling. Everything is controlled by Microsoft software and I was under pressure to use Publisher. Am not prepared to waste time learning MS stuff when I can already use Scribus and pdfsam. I would expect them to be able to save the file and then cut it up to suite their process but apparently not. A friend with a Mac receives a copy and reduces it to a few hundred Kb for posting on our website and he has no problem but he's using a unix-like systerm of course and I send it to him via email. The printers wont accept it by email - some thing to do with their security set-up; no I don't understand that either!
Will try formatting a disk - thanks for your inputs,