Have you recently opened and then closed the fridge (over the last 1-5 minutes)? If so, being unable to open the fridge again right away is an indication that your door seal is working well. An example of this is you open the fridge, grab a yogurt then close it, but then you decide you want a pudding so you try to open it again but the door seems stuck.
When you opened the unit the first time for the yogurt, heat and humidity entered the fridge. When you closed the fridge, this heat was sealed into the unit. If you go to open the fridge again within 5 minutes for the pudding, it might be difficult to open the seal. Wait 5-10 minutes (this allows the hot air in the fridge to cool), when you try opening it again there should be no problem.