Root exit without any warnings or errors

I tried the following commands, and root exited without any warnings and erros.:

root [] f=new TFile(“monitor.root”)
root [] mon=(TTree *)f->Get(“monitor”)
root [] mon->Draw(“phm:psdm”)

Then I tried “gdb root.exe” with above commands, I got this error from GDB while root terminated:

Cannot find user-level thread for LWP 20457: generic error

What does this error mean? I have no idea about it. Please give me some hints.

I checked the memory information and found that a process almost took all of the memory: winbind! My PC has 512 MB memory and winbind took 800 MB. The error was caused by memory full.