The accolade ceremony often involves a sword tapping either sword of the person being knighted. Is there any evidence of one of these ceremonies going horribly wrong?
No. The accolade has its roots in what was actually a physical gentle blow with one's hand against the neck of the recipient as a sign of both service and virility -- i.e. a knight could "take a punch" and also demonstrate his humility to both his ruler and, by extension, to God by proxy of divine right. The accolade eventually transformed from a hand into a sword in order to emphasize the military aspect of the ceremony. I've read that the transition to the sword was in part due to an attempt to slightly nick the knight to ceremonially demonstrate that he was willing to spill his own blood for the state, but this to me sounds like a bit of Victorian kitsch.
At either rate, England was the first country in Western Europe to use the sword in the accolade with later nations, such as Prussia, electing to use the sword in an accolade in imitation of the English ceremony. In France, Spain and Portugal, however, knights continued to receive the physical accolade which eventually became a kiss on the left cheek followed by the presentation of a sword or badge of office.