However, his derivation of his cogito came about as a result of his "Evil Deceiver" theory--he could not know anything for certain, because there might be an "Evil Deceiver" that led him to hold whatever belief it might have been. However, he doubted those beliefs, and did not believe that an Evil Deceiver would try to convince him of something and then try to make him doubt it. His cogito might as well have been a dubito--"Dubito, ergo sum." I doubt, therefore I am.
It doesn't really matter--this is still just as flawed as his initial cogito. If there were an Evil Deceiver, then making him doubt his beliefs may well have been his initial intent, and we're back at the beginning.
A great book that has a tangent related to this can be found by clicking on my title.