can't defrag my system

I went into accessories and system tools and tried to do a defrag and this error popped up:
Microsoft Management Console
MMC cannot open the file c:\windows\system32\dfrg.msc
this file may be because the file does not exit, is not an MMC console , or was created by a later version of MMC. This may also be because you do not have sufficent access rights to the file. Can any one help me?

HI
log in as an admin

try this: my computer - right-click drive c - properties - tools - defrag

or navigate to : C:\WINDOWS\system32 and search for dfrg.msc ( make sure that you see the hidden files too )

or install a free defrag-tool ( Auslogics for example - fast and free )
Regards