In my experience, there are only two main reasons why Toast 18 would crash on launch:
1. The installation is corrupted
2. You have a device attached to your Mac that Toast doesn't like
The second reason is the one that gives the most headaches when helping other users, because they do not give you all the info you need. Then you realize while reading their system report that they have one or two hardware devices attached, like maybe a digital sound mixer, a Canopus docking station, or a USB capture dongle, etc.
If you have already tried doing a clean install of Toast 18, and it is still crashing, check if you have any peripheral devices attached to your Mac - pull them all out, then try launching Toast again. If it launches this time, then one of those devices is causing the trouble.
Well, obviously it would be easier to disconnect your peripheral devices first, than do a clean install.