I upgraded from Sonar platinum (purchased outright a year or so ago) to the new subscription based platinum and I can't seem to open any of my projects, even in X3 producer?  
Running Windows 7 home premium 
i3 , 540 @307 ghz
16 gigs of ram
64 bit

Here is some history here which may provide insight to those reading this post.
I suspect the Platinum upgrade/upgrade with lifetime updates issue is not what you really want to address at this time, is it? It is not clear how you are opening projects. Do you start SONAR and use the Start Screen or are you launching projects from Windows Explorer?

Yep I am launching sonar from the icon in my desktop then (in most cases) clicking from the recent projects list and it hangs.
 
I am not all that upset about having to upgrade Scook.  I am irritated with paying money and having my whole system become unstable and Sonar become operable, even in older versions that were rock solid.

I don't suppose there is a backup your can restore.
 
 

Just a couple of more things. From your PM
How to rename aud.ini:
AUD.ini is located in c:\Users\[your user name]\appdata\roaming\Cakewalk\SONAR Platinum
rename it using Windows Explorer and restart SONAR. This will rebuild the file.
 
This describes how to use the Windows Event log http://www.sevenforums.com/tutorials/226084-event-viewer-open-use-windows-7-a.html
 
After simplifying your hardware config, did you try opening projects in safe mode?

standby...  I think you are onto something there Scook.  
Well yes I tried in safe mode and it still hung up, I just renamed the Aud.ini file and reopen sonare and 1 project did open!   I am exporting a mp3 I really neede now and will try the others including the one that started all of this mess in a few minutes.  I suppose I should also rename the aud.ini  for x3, x2, and 8.5 as well then huh?
 

There is a user directory with an AUD.ini for every version of SONAR.

Scook, Thank you so much.   I was gritting my teeth down to a nub here man.   You are awesome sir.

scook
Just a couple of more things. From your PM
How to rename aud.ini:
AUD.ini is located in c:\Users\[your user name]\appdata\roaming\Cakewalk\SONAR Platinum
rename it using Windows Explorer and restart SONAR. This will rebuild the file.
 

This worked like a charm.  Not sure how to mark this post as helpful, but thank you again!

It was flagged as best answer a few hours ago and somehow was reset. I put the flag back. 
That is not as important as the fix though. Glad it worked for you. If you want to work the upgrade issue create a new ticket with sales for it. If you need to do a follow-up thread, please post it in the Cakewalk store area http://forum.cakewalk.com/Cakewalk-Store-f79.aspx