PowerPoint Upload stops at 59 percent

The most likely reason for this issue is that you either have one or more corrupted slides in the deck that are stopping the import, or perhaps some object on one of those slides is responsible.

The solution is to just try importing small groups of slides until you find the group that will not import, and then use a process of elimination to find the offending slide or object.  Once you do, remove it from the mix and substitute with something else.