Apple Macintosh System 7.5 - Manual (Page 87)

Difficulty modifying the System file
Problem: When you try to use the Installer, you see a message that the
System file cannot be modified (or repeated messages asking if it’s okay to
modify the System file).
Cause 1: You have installed virus-protection software that guards against
modification of the System file.
Solution 1: Turn off your virus-protection software by dragging it out of the
System Folder and restarting your computer. You can turn the virus-protection
software back on after installation.
If you are installing from floppy disks or a CD, you can also try disabling
your extensions by holding down the Shift key while you restart the computer.
(If you are installing over a network, you must leave the extensions on in
order to connect to the network server.)
Cause 2: Your System Folder may be protected. Or the System and Finder
files may be locked.
Solution 2: To turn off System Folder Protection, go to the Performa or the
General Controls control panel (depending on your version of system
software). To see if your System file or Finder file is locked, select the file’s
icon, then open the File menu and choose Get Info. To unlock the file, check
the Locked checkbox to remove the X.
The floppy drive on your Macintosh Plus, Mac SE, or Mac II doesn’t recognize the
installation disks.
Problem: When you try to begin installation, your Macintosh does not
recognize the installation disks.
Cause: The floppy disks are 1.4 MB disks. System 7.5 components are not
available on 800K floppy disks.
Solution: Install System 7.5 components using a CD or install over a network.
83 Troubleshooting