jag, that's a tough one. The only time I've ever gotten that "out of memory" message is when I've tried to bring in M4p's from like iTunes or whatever the heck that file extension is called. They are encoded a bit differently or something and Sonar won't read them unless I use this other software I have to turn them into regular mp3's. But that's the only time I've ever experienced the out of memory message.
You should be able to just install X2 (the program only) over top of the X2a update. It's worth a try though I can't promise you it will be a fix. Just go to your X2 install and select "custom" install. This way all you'll install is Sonar without all the plugs and synths etc. From there, make sure you at least get the hotfix patch for the original release of X2. The hotfix really controls crashes and inconsistencies. If the hotfix gives you issues and you had no problems with just stock X2, go to C:\Program Files (x86)\Cakewalk\SONAR X2 Producer (if you installed 32 bit Sonar) or C:\Program Files\Cakewalk\SONAR X2 Producer (if you installed 64 bit Sonar) and you'll see a folder there named "Backup".
In this folder is the original Sonar exe. Copy it and paste it into the directory where the backup folder is in, which is one of the directories I mentioned above. You'll see another SONARPDR.exe and it will ask you if you want to replace it. Say yes.
Keep in mind, the above will only work if you install Sonar X2 from the original release, then apply the hotfix. The hotfix is what creates that "backup" folder and puts the original Sonar exe in there. So when you go to that folder and copy and paste the exe back into the correct directory, you are removing the hotfix and going back to the original release of Sonar X2. Hopefully though, just re-installing Sonar by itself and then putting on the hotfix eliminates your issues. That hotfix really helped me out with Pro Channel crashes, so it's worth a try to put it on after you install Sonar. But if it fails, you can revert back easy enough.
Worst case scenario, totally uninstall Sonar and reinstall. Though it sucks, it may be the only way to go unfortunately. Good luck.
-Danny