One user has a blank screen while trying to modify or add a post

Hi,

I have one user of my site that can't modify or add post to our blog. The bug is recent, it happened like a week ago, before that he posted regularly. When he click on a post it direct him to a blank page, but the weird thing is that I tried the same on my computer with his account and it worked for me. Plus, when he use my account on his computer it works.

From what I saw on other forum I tried changing the user group, reactivating facebook access, changing browser ( It doesn't work on any )...

So, have you ever seen a problem similar to that?

Thanks for your help it's really appreciated.