Dynamically generated PDFs not showing in certain browser

I use Ezpdf to generate invoices in pdf format. Last year everything was fine. Nothing has changed from the ezpdf code. Pdfs showed up on PC and Macs with no problem. This year, on certain browsers, a white page is shown instead of a pdf. To show how picky this is. On two macs (safari and Google) pdfs are generated perfectly. On another Mac the pdfs only show in Firefox. On certain Pcs they only show in Firefox but with misaligned margins at the top of page. I was wondering is anyone had come across something similar. Thank you.