If you have a license for 4D Developer Edition and attempted to run 4D Compiler under the classic environment, odds are you faced a serialization dialog which did not accept your developer edition serial number. To work around that problem:
1- Restart your machine under OS 9.x.
2- Launch 4D in demo mode and open or create a database.
3- Press CTRL + Shift + F8
The Serial number entry dialog is then displayed.
4- Enter your Developer Edition Serial number and quit 4D.
You can now restart your machine under OS X and use 4D Compiler in the classic environment.