I saw some code trapping Exception in the MultiDisplayScanner family.
That might be a source of problems.

2009/12/28 David T. Lewis <lewis at mail.msen.com>:
> On Mon, Dec 28, 2009 at 01:22:05AM -0200, Casimiro de Almeida Barreto wrote:
>> Ok,
>>
>> I started with a fresh image (Squeak3.10.2-Trunk-091128.zip) and
>> updated. Then I reinstalled some packages (FFI, OSProcess, OSProcessIO,
>> CommandShell, Balloon3D) and the problem disapeared.
>>
>> Last image had installed VMMaker, Speech and other packages. I'll try to
>> reinstall everything in order to see where the problem arises).
>
> There is definitely a problem somewhere. I have a broken image with the
> same symptoms that you are reporting. In my case, it happened when I was
> trying to save an update to the squeak trunk, so I was expecting that it
> was something related to those changes (the large changes file updates).
> But maybe that was just a coincidence.
>
> In any case, I can confirm that this same problem has happened one time
> to me. Unfortunately that I cannot reproduce it in other images, and it
> is hard to figure out what is wrong with the broken image because all the
> debugger windows have the same "red X" failure.
>
> Dave
>
>
>