Instruction at referenced memory xyzxyz at the memory could not be written.

This error occurred in a friend's PC running Windows XP Service Pack 2.

The error occurred frequently while running different applications and even in the background.

I also received a similar message about the memory could not be read.

There are a number of suggested answers to this problem kicking around the Internet.

I tried disabling DEP. This seemed to stop the "write" error messages but I still get "read" error messages. The system is slow, I have been told that networking does not work and that plug and play does not work I tried plugging in a USB key, and this took ages to install and detect.
I may have to use system restore.

I should test the physical memory first.
Download and write to CD the bootable ISO with Memtest86+ from Memtest.org
1) Try running Dial a fix - down load here
2) It could be a bios problem - check with the Sony website for specific information.

I ran the memory tests and it reported no problems.
I then ran chkdsk /F and it found problems it could not fix. Running this a couple of times before windows started did not help. I also found Event Viewer messages that showed problems accessing the hard drive. I am thinking that the hard drive is to blame and am going to replace it.