Make sure you have--and are using--only one copy of the official installation utility, "Installer" v44.10 (10/01/99) or later. This should eliminate most script problems encountered during installation, including possible errors with the "MakeDir" command. Officially, Installer should be in your SYS:Utilities/ drawer, but it will also work fine in your SYS:C/ drawer. You can use the Workbench menu item "Window/Find..." to check SYS: for the location (and possible duplicates) of Installer.
Other tips
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