recent instability

In article <444774D0.7080306johnrshannon.com>,
John R. Shannon <johnjohnrshannon.com> wrote:
>-=-=-=-=-=-
>
>Steven M. Bellovin wrote:
>> Two days ago, I upgraded to 3.99.18 from 17 April. 
Since then, my laptop
>> has frozen once and spontaneously rebooted once. 
Has anyone else seen
>> that sort of instability?
>> 
>> 		--Steven M. Bellovin, http://www.cs.columbi
a.edu/~smb
>
>Yes, on a dual Xeon machine I'm seeing lockups per day.
I'm unable to 
>get any indication of what is causing the problem.

What was your last working kernel?

christos