In message <75ff70b0509080748ded4020@mail.gmail.com>, Onno Ebbinge writes:
>> A disturbing thought, since I recently added more RAM to the machine.
>> Memtest found no problems in a single pass; maybe I'll run it longer
>> overnight.
>
>I had a similar problem and used memtest. Here are two tips:
>- Use memtest from http://www.memtest.org/ and NOT from
>http://www.memtest86.com/.
>- In Test selections use "all" instead of the "standard" default
>selection, this one saved me! The "standard" test did fine, the "all"
>test revealed timing problems with one of the memory chips (no
>overclocking) on the module. Underclocking my memory solved my
>problem.
>

I couldn't find any such option, but it didn't matter -- memtest86+ 
(from the site you suggest) found some errors.

Thanks!

		--Steven M. Bellovin, http://www.cs.columbia.edu/~smb