Update fails for "case sensitive", but my fs isn't

I know I ran into this before, and found a solution, but now I'm drawing a complete blank and Google isn't even pretending to help.

I'm trying to install an update for Acrobat 2015 onto a Mac that's identical to several other Macs that have this patch installed, and the file system is NOT, I REPEAT **NOT**, case sensitive.  Yet the installer fails claiming it is.

How dow e get around this?