Ok i think there is no need for further research, the problem is solved now for me coz of description from [edoneel].
I read already that there are some generic error codes and normally we should call a special error-function to get the real error description. But i think this can be done only in virtual machine directly after the command that produces the error. I remember that from Windows, where you need to call GetLastError() immediately. Maybe it would be useful to have a possibility in Smalltalk to delegate that full-error-description to the image and then it can be shown in debugger instead of just a generic error message.