I downloaded the following file: Lightroom_4_LS11_mac_4_3-1.dmg.mdlp from the Adobe site. I click on the file and it launches Matlab.....huh?? What do I do with that? Sorry, just switching to LR from Aperture, so be gentle.
First of all check the file size of LR, it should be around 419 mb. If not, then the download might have not been completed successfully. You might want to ty downloading the same again from a different browser.
1. Download and install free preferencepane RCDefaultApp from http://www.rubicode.com/Software/RCDefaultApp/
2. Under tab Appl., find application DiskImageMounter
3. Check UTI "com.apple.disk-image-cdr"
This should suppress your problem.