Ok,
Please answer the following questions
1) What type of system do you have? HP, Lenovo Dell etc.
2) What fixed disk test are you running when you receive this error? Controller, linear verify, SMART etc.
3) Do you receive this error consistantly? Do you get it every time you run the test?
4) Do you receive an error in both DOS and Windows? Have you tried Both the PC-Doctor for windows and PC-Doctor for DOS programs and do you see errors in both?