I was struggling with this issue of upgrading a 3.6.2 site on a WAMP / localhost install. I would select to upgrade, Akeeba backup ran, the upgrade would crash with percent done as “NAN” or “not a number”.
The fix was the “tmp” path and manually install patch. For a localhost install the path needs to have both “\” for the local part and “/” for the server part of my machines environment.
I wasted hours on this. I should have checked another localhost install sooner.
The other part was to go into Components >> Joomla! update >> and this time do a manual “Upload & Update” process. You will need to download the 3.X to 3.6.4 upgrade and install this.
Before I could upload the package I was warned about two PHP.ini settings of post_max_size and upload_max_filesize had to be the same. I set them both to 128m.
Before I ran the update I removed Akeeba so it wouldn’t run another backup before the upgrade, but I learned when I went into Extensions and Manage that I could just select and choose “disable”.
I really hope this helps someone else out there…