Hi Dan
Thank you for your reply.
Just to confirm - 2 computers sending the same file to to same printer.
Computer A printed the top left logo at 70% opacity and the photos in bright colours. I got involved to sort out the problem with the logo and re-saved the file with it set to 100% opacity. When I printed it from Computer B, the logo was fine but the slide photo was much darker. We then tried printing from Computer A and . . .
Just spoken to my colleague and it transpires that he was printing it as a PDF as he was getting an error message and the program crashed. I have now reported it.
Now I just need to work out what is going on with the opacity setting when printing via PDF - any thoughts?