I am getting a similar error on a Windows 7 64-bit machine. The update process wouldn't initialize because there was some access error. After I uninstalled and reinstalled Archicad 14 it took the latest hotfix.
However, I just tried to install the last library update and it give the same error that I got before.
It is not my workstation but we have 5 Windows machines with nearly identical software configurations that had no problems with the update.
iMac - 2.93GHz Core i7, 4GB, OSX 10.6.7
ArchiCAD 15