Pentalobe Screw: can't put it back

Hi guys,

First, thx to all the iFixIt team and community, every time I need to fix or replace something on my iPhone 5, I found all I need here and that's pretty cool (without saying pretty bad @%^ to say I fixed my phone by my self!).

Anyway, yesterday I decided to move a little bit further and replace my old rear case with a brand new one. It took me 1h but finally everything is back in place and working fine, my iPhone is like brand new. But, there's always a "but"...

I can't put back the left pentalobe screw. I tried the original screw from Apple, + 2 sets of 2 screws I bought online, I can't screw it at 100%, it's like something is blocking the screw to get back in place totally, which is strange because the screen is perfectly put into the case.

I don't know what's causing this and how to fix it. Is there every one who faced this issue?

Thanks!