Membership not updated after payment ?


I have a critical problem with membership2 pro plugin.
When a member pays for a membership ("Alumni" on my website for example), the paypal payment works well (I can see it on my paypal account) but the new membership is not given to the member (and the automatic email is not send)... If I want to give the membership status to the member I have to do it manually from the administrator website.

Can you help me to fix this problem. I give an access !

Thk a lot for your help.