|Ok. I already moved everything to one folder and changed the batches to eliminate the problem, but I'd rather solve it the right way.|
Here's what it used to look like:
The master batch would be in <usb drive>\pctools\enhancements\apps:
set /p drive="enter root drive of the install batch file: "
_7zip.bat would be in the same folder:
start /wait "%drive%:\pctools\enhancements\system\7z920.exe" /S /d="c:\program files\7zip"
But I tried other permutations in the slave batches, as I wrote in my OP - expanding the quotes or CDing over to the target folder first instead of using the long filespec in the Start command - with all of them running into various problems.
I've even run into problems with quotes when the target executable is in the same directory. For example,
would run into problems, but eliminating the quotes would solve them. I have no idea why that is the case.