control panel

[leon a]

i have installed a series of patches and softwares...in no
perticular order...now i have a problem with my control
panel...i don't know if it is misconfiguration or a
virus...i scanned and found none...and downloaded the
msblaster worm patch....so i try to click on any icon in
the control panel..and i get rundll32.exe is not a valid
application error....why?
if i have to do something that will replace certain
files...will this mean that the software installed won't
work any longer ( require a re-install) ???