Try this:
- Download Wavelab LE (www.steinberg.net/getwavelabLE)
- Register the software and get the activation code
- Download the latest version of the eLicenser and run maintenance.
http://www.elicenser.net/en/latest_downloads.html - Download and install the Steinberg Application Installer Tool for Yosemite
https://www.steinberg.net/en/support/content_and_accessories/content_and_accessories_saitfy.html - Install Wavelab LE as a trial version
- Quit Wavelab
- Run the eLicenser software and activate Wavelab
Wavelab should now run OK on Yosemite.