My partner's machine recently came up with this, referring to
ESDI_506.VXD, which is associated with the hard drive.  It has had
other unreproducable intermittent problems in the last two weeks,
often when a program tries to access the hard drive.

  My initial theory was that the hard drive upgrade that I had been
putting off should be installed while the old drive might still be
accessible.
  When I got the machine open and fired it up, I noticed something
rather scary.  If I moved the power lead for the CPU fan around, the
fan would slow down and speed up, and when it sped up all the way,
the hard drive would "wake up".

  My revised diagnosis is that the power supply has become
unreliable and/or inadequate.  This is something that others seeing
this kind of symptom should probably be aware of and check.

David G