Printerhelper & PDFCreator V5.1.1 crashes on install (Earlier Versions work)

During a recent upgrade to V.5.1.1, PrinterHelper.exe crashed and will not install. I've uninstalled and reinstalled with no success.

However, I uninstalled and installed V. 4.4.3 successfully and it works. (Except that it will not autolaunch when printing the first time). I would launch PDFCreator and then it autolaunches.

This is happening on Windows 7 Ultimate systems (and not all of them). Any help would be greatly appreciated. Thanks.