Attempting to upgrade Mac OS Classic 7.5.0 to 7.5.3 via floppies that have been tested successfully on a Performa 460... but things fail ominously on my IIsi with "This is not the correct "⟨SrcDisk⟩" disk. Make sure you are using the original Installer disks and try again. Click Continue if you have the correct disk to insert. Click Stop to stop any further installation."

[![eIIsi install failure](https://i.stack.imgur.com/lee93.jpg)](https://i.stack.imgur.com/lee93.jpg)

Some kind of copy protection? What gives, these install floppies just worked yesterday on a Performa 460 just fine, where is this error coming from?