Problem with error rate calculation

Hi! I have built a "BPSK modulator-channel-BPSK demodulator" model in Simulink. The input is a Bernoulli Binary generator. This is then modulated, distorted by noise and demodulated. At the output of the demodulator, I have a waveform representing the bits received (continuous both in time and in amplitude). In order to make it discrete in time and in amplitude, I use a sample and hold block, which samples the aforementioned waveform at the middle of each bit period. So, at the output of the sample and hold block I have the waveform of the bits received (which starts at 2.65 sec and the bit period is 3 sec and is discrete in amplitude - 0 and 1). At this point how can I calculate the BER? I tried to use the error rate calculation block, but when I connect the output of the sample and hold block and a delayed version of the initial bits (by 2.65 sec), then I get the following error message: "all sample times for this block must be discrete. Continuous sample time is not allowed". What should I do?