You can find some of them in the header files. I think your examples are reversed and they should be CANT and !MSG. CANT is in ASTypes.h
#define kCantHappenErr 'CANT'
Which isn't very helpful!
Weird, I had Xcode display the error codes as char bytes, but they do make more sense reversed. Considering that and the problem with CS6 Mac cursors, the error codes CANT and !MSG do make some sense. Thanks for the observation!
The best way to retrieve more informations about error codes is to parse header files.
You will find all of them. It takes some times to find the correct header file!
When an error raised, if I do remember correctly, you should have an decimal value.
To get a more readable value, you just have to convert it to ascii. (decimal -> hexa -> ascii).
It saved my life more than once.