the first cure for this error I found, described the HP engineer removing and then reseating the memory which cured the fault.
If you do this, the pc must be OFF and remember the importance of earthing yourself as static electricity is a killer of electronic components!
I always look for the simple answer first, and more often than not it is the cure.
As a matter of interest, where are you based? I am in Hammersmith, West London.
Good Luck - Keep us posted.