LW 3.4.7 from my Pro page worked as expected yesterday, so the installer seems fine.

If you wanted to try something more while waiting for a Pro Support answer . . .

perhaps the old installer was cached or used from the HD--search for anything containing "LW" on your HD and delete them (if you delete the preferences folder too you'll really get a clean start, but will have toreset your prefs and wait for all your shared files to rehash on the next startup). Clear your browser cache (safari?) and go to your download page to try again.

Cheers