Male having "bedroom" troubles...

Alright, I have never had a male do this before and I have had several males. My guy is court-shipping and even chasing, but he is biting the female's neck rather vigorously. Then, he lets go and he just looks up like he forgot what he was doing or he can't go any further. I have had males that just don't want to breed and he wants to. I am wondering if something maybe interfering like the paper towel or what, but they are both healthy, they have been examined and everything. The male is larger than the girl and both are of breeding size. I am getting concerned for my girl I don't want her neck getting torn up. I have tried introducing to each others enclosures and a neutral enclosure, but I have never been one for rooming for a week or so...I like to witness the lock then separate so my females aren't getting to stressed. So anyone have any ideas why the male just stops?
Any input would be appreciated.
Thanks,
Owen

He sounds immature. How old is he? How much does he weigh? What kind of environment do you have them "breeding' in?