There is apparently an extension conflict between the Be "OS Chooser" extension and Apple's CD-ROM drivers. This is clobbering the Apple drivers.
Using an extension manager, or by renaming the files in the Finder, ensure that the Apple CD-ROM driver loads before the OS Chooser extension. This should solve the problem.
If it does not, try disabling the OS Chooser extension entirely. You will no longer be able to boot directly into the BeOS, but you will still be able to use the "BeOS Launcher" utility in the Finder to start the BeOS.
Time-saving tip: If you hold down the Shift key when booting the Mac OS, the Finder will load much faster, and you can use the BeOS Launcher that much sooner. After all, if you're not going to use the Mac OS, you don't need those extensions...