Maybe your path or environment is mucked up

http://www.computerhope.com/issues/ch000549.htm

As I have stated before...some times the fastest easiest and surest way to fix a buggered install...is to format and reinstall

MLF

edit more on path problems

http://support.microsoft.com/kb/180410/en-us

http://support.microsoft.com/search/...ode=a&x=13&y=9