I came on here looking for assistance with this problem but maybe I can offer something. Initially I could not even install 17. After contacting "Service" multiple times, I was advised to delete all Toast 17 files and re-install. 4(!) clean re-installs later with progressively more detailed instructions each time they finally suggested setting up a new admin account and installing there. That actually worked (shock!) but they can't tell me why it won't install on my usual admin account. "Incompatibility with some of your files". But they can't or won't tell me how to work out what files are causing the problems.
Currently, my workaround is that I have to log out of my own system and log in to the new admin account in order to use Toast. Which is more than a little irritating...
I cannot tell you how unimpressed I am with Corel's Support staff. As noted elsewhere in these fora, I don't think they actually read the help requests very closely at all, but just reply with 'boilerplate' responses.
So, I have a workaround but if anyone can suggest a solution I would be grateful.