jac39

I am using Xp on a Dell pc. It has 512 ram 1.59 ghz Pentium 4. I downloaded Defraggler two days ago. I ran it and it worked find the other day. Today I was running it again and it got to 83% and then a message appeared from microsoft that Defraggler had encountered a problem and will shut down. What might be causing this problem? I downloaded to my other pc compac which also has xp and it works find. Jac39