The freeze issues are all symptoms of the same issue where the project ports are being assigned to unexpected values. 
The loss of audio can be rectified by simply reassigning the ports as some others have posted.
 
I think another possible solution is to RENAME the new EXDrummer dll AND additionally keep the old EZDrummer dll. To do this you would have to backup the original vst dll PRIOR to installing the new version, and then rename the new dll to something else before restoring the prior version. After a rescan, old projects should load the old version and new projects can use the new version. Something along these lines is the only solution that can be done from the plugin side.

konradh
PS Interesting that I was chastised for saying Toontrack was not responding so I said "OK, Cakewalk is not responding" and then I was corrected again.  I'm not blaming anyone, but it certainly isn't my fault!

Sometimes I'm too chicken to quote people but I would not have quoted you. I was observing just the usual Chinese whisper effect that often happens in posts like this, it didn't get too bad and my point is totally irrelevant now. Ta.

It is remarkable that Toontrack's Sonar beta testers didn't pick it up.

I will add one other thing. When I contacted Toontrack and Cakewalk about this issue, they both asked for more information.

I sent that in, and since then have had emails from Cakewaalk, as well as PMs from staff members on here, explaining what they were doing.

Toontrack did not even have the courtesy to acknowledge my email.

I don't think these reflect well on Toontrack.

jb101
It is remarkable that Toontrack's Sonar beta testers didn't pick it up.

I'm sure if you were to offer your services they would consider you for the team.

cecelius2
I have a question about this bug as I am preparing to purchase EXD2 soon.  Does this bug occur on new projects also, or just on ones where EXD1 was present?

No, this only occurs with people who use EZdrummer (1) and have other softsynths in their SONAR projects and then upgrade to the new EZdrummer 2.  New projects are not affected after the upgrade.
 
I haven't tried this but but I have a feeling it would work:
 
If you have EZdrummer projects that you suspect you will want to access and modify in the future, create a midi track and copy all of the EZdrummer midi clips into it.  Delete EZdrummer from the project and save it as a new project.  When you have all of your projects modified then upgrade to EZdrummer 2.
 
Or you can wait to see what sort of solution the EZdrummer 2 developers come up with.  We have managed to open up the back door channels of communication and hopefully it won't be too long before something can be worked out.
 
Or you can choose not to upgrade to EZdrummer 2 or move to another product.

jb101
I will add one other thing. When I contacted Toontrack and Cakewalk about this issue, they both asked for more information.

I sent that in, and since then have had emails from Cakewaalk, as well as PMs from staff members on here, explaining what they were doing.

Toontrack did not even have the courtesy to acknowledge my email.

I don't think these reflect well on Toontrack.

Don't be too tough on Toontrack; Cakewalk is the exception, not the norm, and is unusually responsive given the company's size. FWIW I spent last week in Boston and was involved in several meetings. The company looks at everything through the lens of "what's best for our customers?" Obviously part of that is the belief that happy customers are good for business, but because most of them are musicians who use Sonar, I think a lot of it is because they live in "our" world.

Noel, Great info, although I don't know how to reassign ports on an instrument I can't unfreeze, so I don't see how that resolves the audio issue.  The other tricks you suggest sound good--I just need to get up the nerve to reinstall EZD2.
 
CakeAlexS, I was only joking around about being "chastised."  Feel free to quote me, correct me, tease me, give me a hard time, or whatever.   We are all friends here and I was just smiling about the back and forth on this topic.

Kind of interesting that this thread is still going on and it is the same info going back and forth.  Toontracks fault, Cakewalks fault.  I am at a point where I just don't care who's fault it is.
 
I do have one alternate fix I am thinking of trying.  I recently upgraded from X1 to X3 because of the ridiculously low upgrade price Cake just offered (thanks to Cakewalk for doing that by the way). 
 
Anyway I am going to try to install a second instance of ezdrummer1 in a different file than the original install then apply the upgrade to the new file path of the second ezdrummer1.  Hopefully it will only override the new install.
 
Then I am going to try to get ezdrummer2 to upgrade the second instance of ez1 and put that .dll in its own folder and direct X3 to scan that folder for the vst (and not scan for the original .dll). 
 
X1 will still be scanning for the original EZ1 .dll and X3 will scan the new folder for the new EZ2 .dll.  Not sure it will work but who knows.

StumpyV
Kind of interesting that this thread is still going on and it is the same info going back and forth.  Toontracks fault, Cakewalks fault.  I am at a point where I just don't care who's fault it is.

 
Please refer to post #65. Sonar would have to do a lot more work to accommodate EZD2 than the other way around. Note that this is also an issue with the VST spec, because Toontrack is using the same ID as for a previous product, even though they have different characteristics. But if they change the ID, that creates a different set of problems.
 
With Cakewalk not being on their beta list, Toontrack's testers need to find incompatibility problems. If enough people asked Toontrack to add a preference that allows specifying the number of outputs and they implemented it, problem solved. Meanwhile, several workarounds have been offered
 

I do have one alternate fix I am thinking of trying.

 
Let us know how it works...

I think plugin manager is a "shared" utility. Please keep us posted as to your results.
Tom