Now the problem has become worst, after 12 hours of simulation the Window Manager (Metacity) dies, X dies and my application not founding where to write dies of SEGFAULT!

The impression is that the MessageBox are the problem as in our log you see that one of them is created, then Metacity dies... the same, identical object was created a 1'000'000 of times before.
I've verified: the MessageBox is created on the stack and so it is deleted when the function returns from the exec() method... so "by design" it shall be only one... but IMHO the WM seems to have a limit to Windows he can show!

He not find "an exit": when the application lost more memory it was more stable, if OOM not killed it... it worked forever!
Now it is the OS itself that dies without an apparent motivation...