Can't Locate Disk Defragmenter

[Foy]

When i try to start disk defragmenter in windows xp, a
message appears,( mmc.exe-unable to locate component)This
application has failed to start because xprt.dll was not
found.Re-installing the application may fix this
problem,end of dialog message.If anyone can help with
this problem,i would be mighty thankful for the help.If
it is of any help i am running Windows XP Home Edition
SP1,i don't believe it's the installation of SP1 because
i installed it about six or eight months ago,this problem
has just started.
Thank You
Foy