Launcher & installer not playing nice with Windows 7

I'm having a problem with Portable Apps Launcher on a relatively new 64-bit Win7 install that I think is the fault of the host OS. I didn't note the launcher version I was using but I know I had updated it within the last two months.

I ordinarily start it from a batch file that does some housekeeping before starting the launcher (offers to update the ClamWin definitions, etc), but the batch file kept erroring-out with 'PortableAppsPlatform.exe is not a valid PortableApps.com release and can not be launched.'

I've been using the same batch file to start the launcher for years but my first suspicion was that this new Win7 build's environment was somehow different and that difference was screwing with my batch file, so I tried starting it from CLI.

If I entered the command "start" with no extension, it opened a second instance of Command Prompt. If I added the extension, I got this:

F:\PortApps>start.exe
The system cannot find the file .exe.

Out of sheer stupidity I tried it again with quotes around the command, including the extension ("start.exe") but still got "The system cannot find the file .exe".

Then I tried the command syntax used in the batch file, slightly modified on account of being in a different directory, and I get this:

F:\PortApps>start /D . .\Start.exe
Access is denied.

??????????????????

So I searched this forum and found there were a few similar occurrences, but in each case Mr. Haller replied that it wasn't the app's fault but suspect malware, permissions problem, damaged SD drive, etc. To rule out those possibilities I downloaded a fresh copy of the latest PA Launcher install file (v16.0), reformatted the thumb drive and tried to re-install PA Launcher on it (on the same Win7 PC) but the installation kept failing with:

Error opening file for writing:

F:\PortableApps\PortableApps.com\PortableAppsBackup.exe

Which started me thinking the host OS might be the problem so I tried installing PA Launcher from 32-bit WinXP. And it installed no problemo and, once installed, the launcher started fine and the few apps I ran from it executed normally.

So I put the thumb drive back in the Win7 system and it's still doing the same crap, launcher won't start, same errors. Just for giggles I ran a virus scan on the SD drive and it comes back clean. Which you'd think it would have to, seeing as I just formatted it and there's nothing on it but a fresh install of PAL.

To altogether rule out the SD card, I tried to install it on another of a different brand and once again I get "Error opening file for writing:" trying to install the launcher. Which pretty much convicts the OS.

FWIW, it's Win7 Pro, build 7601, revision 17514. My user name is in the administrator's group and UAC is completely disabled on this PC. I have used the same thumb drive I was using initially a number of times on other Win7, 8.1 & 10 PCs, always started with the same batch file, and never encountered anything like this before.

So my question, obviously, is has anyone seen anything like this before, or know how to cure it?

And BTW, for the Mods, I hate reCAPTCHA like it was cancer. I wouldn't even have come here to post this if I had known you were using it.