Fixed it! Same problem exactly, spent 3 hours on hold and eventually talking to two layers of customer support whose only solution was to send me a new download file to replace my cd. After install, same problem.
Being familiar with "under the hood" of Mac apps, I watched what was happening in Mac Console while I duplicated the problem with that blank screen. Sure enough, I could see in the code there was an encryption error. So, being suspicious, I checked my 2014 tax return file by opening it in the 2014 Turbotax Application. Sure enough, it was encrypted! Instead of removing the encryption, via File > Remove Encryption, I duplicated the file (File > Duplicate) and then Saved As a new file and named it 2014returnunencripted or whatever you want. Close out the 2014 app.
Launch Turbotax 2015 and begin a new return. When you select last year's tax file, select the new file you created that isn't encrypted. It will work for you.
Turbotax needs to fix their encryption method as well as how they store that 6 digit code in the event that the program crashes and needs to reopen the encrypted file.
