Not all software can run under Rosetta. It's quite possible that Cubase LE is one such example.
From their KB article regarding Mac OS X Universal Binary:
"All applications that are not listed in the compatibility list at the bottom of this text do not run at all or at least not satisfactorily on Apples new Intel based Macintosh hardware."
http://knowledgebase.steinberg.de/94_1.html
Cubase 4 is listed but not LE. You should probably contact the company to be sure.