[Crash-utility] not able to take kdump from kdb prompt

Hi, I am facing issue when I want to take crash kdump from kdb prompt, after system crash my system entered kdb prompt, when i want to take kdump from kdb prompt its giving following error. can you please help me in this. Linux sff7r900lx1 2.6.18-194.el5 #1 SMP Thu Apr 8 11:00:57 CST 2010 x86_64 x86_64 x86_64 GNU/Linux [8]kdb> kdump diag: -18: Invalid cpu number thanks, Praveen