Like others here, I have hit the exact same bug which causes Toast to crash every time when trying to mount a disc image which Toast itself created in .Sd2f format.
Here is the letter I sent support:
My issue is that the "Mount Disc Image" feature of Toast has been broken in Toast 12.
I can create a disc image with Toast, but every time I try to mount the Disc Image (Utilities > Mount Disc Image…). Toast freezes (perpetually spinning icon) and I must force-quit Toast. Toast will then not even launch again until I restart the Mac.
Mounting disc images created with Toast worked fine in my previous version of Toast (11.0.4), but as I am now running Yosemite I can no longer use that version. So I bought Toast 12, and now I cannot mount any disc images, whether they were created with with this new current version of Toast or whether they were created with a previous version of Toast. I am as up to date as I can be: running the latest version of Toast (12.0.1) and the latest version of Yosemite (OS X 10.10.1) on a Mac mini (late 2014 model).
I need your help. I have hundreds of disc images and I need to use them. Please tell me how to mount Toast disc images again!
I'm talking about audio disc images in the .Sd2f format.
Here is the main part of their response:
Thanks for letting us know about this issue. Our engineering department is assessing it to determine whether it is a valid product defect. This process can take some time. When the issue has been addressed, we will send you additional information by email.
I now see from this forum thread that this Toast mounting bug was first reported to the company over 2 years ago, and even though there have been major and minor updates to Toast since then, they still have not fixed this bug! So after 2 years of this their "engineering department is assessing it to determine whether it is a valid product defect." If a program crashes every time when selecting an item in its own menu (Utilities > Mount Disc Image…) which is trying to mount a disc image that the program itself created, I'd say that is, beyond any doubt, "a valid product defect."
I'm not sure why, after 2 years, this company needs more time to "assess" the situation.
My own assessment has shown that this bug exists in every version of Toast following 11.0.4. Unfortunately, if you are running the current Mac OS (Yosemite) then running Toast 11.0.4 is not an option.
Apparently there is no way of mounting these Toast disc images using any other Mac software.
If you are also stuck in this situation, here is a workaround that I've gotten to work. This is by no means an elegant solution, but it's the only way I've found to mount these images in Yosemite (and perhaps Mavericks):
I had installed the current version of Toast (12.0.1) on my Mac running Yosemite. Then, I also put Toast 11.0.4 on my Mac, not by running the installer (which I assume would muck up my current installation of Toast), but by simply dragging the application that was previously installed on another disc onto my new Mac's disc. I discovered that, while you can't run Toast 11.0.4 in Yosemite for the most part, you can use it in Yosemite for the sole purpose of mounting a Sd2f disc image. So whenever I need to mount a disc image I quit Toast 12, then run Toast 11.0.4 and use it only to mount a disc image. Then I quit Toast 11.0.4 and launch Toast 12 again.
Important caveat: Every time I do this switching back and forth between versions I need to re-enter the serial number into Toast 12. What a hassle.
This is quite a Mickey Mouse way to do things, and it's a shame that Corel has put it's users in such a pickle. But at least I can mount my images again!
In the long run I'll probably just have to move away from Toast altogether, as I assume that if Corel hasn't bothered to fix a serious bug in its software for over 2 years, it probably won't do anything about it in the next 2 years.
Please, Corel, help your users out here and at least tell us what you plan to (or plan not to) do!
PS: The workaround that Leif posted above in this forum using OS X 10.9.1 (Mavericks) did not work for me in Yosemite.