Defrag

I cannot open the tool Defrag. I keep getting a message that says.
"c:\windows\system32\dfrg.msw" It does not exist or not an MMC console or was
created by a later version of MMC. This may also be because you did not have
sufficient access rights to the file."

I have had this computer for around 4 years or more. I keep it updated
automatically and don't understand what has gone wrong. I am the
administrator on this computer and the only person who uses it. How can I
get the defrag to work again like it used to.

I recently received a message that I needed to change from Windows xp
professional sp2 to sp3.. I did that.. Is that what may have caused my
problem. Someone out there please help me with the answer to this.. Thanks.