Error statistics (ES) is an important methodological view in philosophy of statistics and philosophy of science that can be applied to scientific experiments such as clinical trials. In this paper, I raise two potential issues for ES when it comes to guiding, and explaining early stopping of randomized controlled trials (RCTs): (a) ES (via its severity principle) provides limited guidance in cases of early unfavorable trends due to the possibility of trend reversal; (b) ES is silent on how to prospectively control error rates in experiments requiring multiple interim analyses. The method of conditional power, together with a rationing principle for RCTs, can assist ES in addressing such issues.