Not sure whats causing it, but you can stop it ever showing its ugly head again:
Click START/RUN, trype MSCONFIG then click OK, once system configuration opens, click ADVANCED, and the put a tick in where it says "disable scandisk after bad shutdown", click OK, OK, then restart when prompted.
You should then never see scandisk again. However if you shutdown incorrectly, be sure to run scandisk- in fact run it on a regular basis anyway.
Next time you wave - use all your fingers