This actually sounds very familiar. I had this error before 
but had different problems at the time. Will try to isolate 
this when it happens again.
/p

Excerpts from Sebastian Spaeth's message of Thu Jun 02 15:40:43 +0100 2011:
> On Thu, 02 Jun 2011 09:16:33 +0200, Sebastian Spaeth <Sebastian@SSpaeth.de> wrote:
> > in python:
> >   list(Threads())
> > 
> > leads to a program abortion (bombing out of python):
> > Internal error: Failed to read timestamp value from document. (lib/message.cc:731).
> > 
> > Can we not crash the app on misformated emails?
> 
> Just to follow up, I cannot reproduce this anymore. It works fine
> now. Sorry for the noise.
> 
> Sebastian