Nokia Lumia :: Calendar Won't Save Appointments In 800?

I'm wondering if I'm doing something wrong.I love the calendar and it an do everything I want it to do bar one thing. When I have appointments that run on the same day each week but then finishes at a certain time of the year the calendar won't save them. I keep getting a message saying something along the lines of the appointment being too long for the time given.

example. My daughter goes to gymnastics every monday between 4pm - 6pm. She started in August and the course finishes in october.I can add the appointment to the calendar, put how long the appt is for and say it's every monday. Then I cahnge the dates to the date the appt started (august) to the date it ends (october) and it won't save it. I had a blackberry before my nokia (yuck horrid thing) and could do it no problem with that and I don't see why the nokia can't do the same.

Am I doing something wrong? I've ended up just adding the appt from August saying every monday for specified length of time but it runs way over as I've put every monday so no end date. This means I'll have to delete it when the time s up and start again when the new dates happen. It's all well and fine to just delete the ones she is on holiday from but I never know when the next course starts back until near the end and I am a busy woman so need to know what's happening when etc in my life.