I will STRONGLY advise anyone to FIRST replace the battery with an authentic one before proceeding to any further investigation. No matter the canon model, try the battery first. I tried all techniques with my EOS 30D (great camera!!) and almost gave up. Then I decided to buy a new battery--I was seriously tempted by the knockoffs because of their lower cost, but I resisted and bought an authentic canon battery. Now, Err 99 magically disappeared, and I and my teenage daughter who shares the camera are again very happy. We took gorgeous pictures today of what scientists bill as the biggest and brightest full moon that we will see in all of 2010.