Yes I was mistaken - after having read the part of the Reason 2.5 manual again it brought back some memories.
Here is what the manual said;
!A NOTE FOR MACOS9 USERS!
In addition to being located in the Reason program folder, an alias for the Reason engine is also
put in the Extensions folder. This allows you, if required to remove the alias. This will prevent
Reason from running in Rewire mode, but will still run fine as a freestanding application.
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I recall ages ago after having installed different versions of Reason, Rewire would not work between Cubase
and Reason and quiting Reason would cause a crash after the graphics shut down. After reading this message
in the manual I opened the extensions folder and found 3 different version of the Reason engine - 1 demo, 1
earlier version I had installed, and the last version just installed. I threw them all out - opened the program
folder, made an alias of the last installed Reason Engine, dropped it into the Extensions folder and all was up
and running again #modified# after a restart and a desktop rebuild. #modified#