Defraggler leads to a blue screen

[Bob3]

I downloaded Defraggler about a month ago. I tried to defrag my entire C drive and it ran for over 10 hours without completing the job. I'm using only 2/3 of the hard drive space with XP my OS. I found that I could defrag individual and groups of files nicely but as soon as I tried one or more of three with over 200 fragments, I got the famous blue screen and the system was frozen. I could restart the system OK but it did not appear to be stable. I have removed Defraggler from my system until I can find out what the problem is. Any ideas? Bob3