MRBS freezing when n-weekly booking made

Hi, when my users make a booking of n-weekly (we run on a 2 week cycle timetable at school) mrbs freezes. I have to restart the WAMP server each time it freezes up. I have downloaded the latest code for mrbs and increased php memory limits (in case) but nothing is working. The weekly repeat type works. I have turned on debugging but see no error.