I solved this problem before couple of months and I has same a problem I ask everyone, do everything, but always the same problem.
How I solved the problem? easy within couple of hours. I already explain in one of my earlier message on other topic. I will repeat here again. I was go from 1.7.7.4 to latest 1.7.8.8.
First download (not direct install or upgrade) all upgrades to 1.7.8.7 in zip files (will be several zip files), then I install first upgrade via One click upgrade BUT CHANNEL is "local directory". Start my shop, make simulation as a buyer, works fine. After that with same way I install one by one upgrade (always simulate as buyer, all works fine). And finally install newest 1.7.8.7. on the same way. Later I normally install (direct install) 1.7.8.8 works fine.
So you must go step by step, one upper installation after another (1.7.4.4 -...-1.7.8.0-...-1.7.8.7-1.7.8.8)
Sorry for my non-native english.