I upgraded from 1.3.7 to 1.3.8 - easy process. I had the same blank page on checkout. I tried every solution I could find - finally - I updated my "optional Shipping Insurance module 2b" to the latest version (3.0) - and suddenly everything worked just fine. I do have quite a few mods added over the past year or two - as of this writing, I think they are all working.