My bad, I missed the part about twinview :/ Maybe you could try disabling twinview and see if X still keep crashing so as to make sure the issue really comes from there ? My computer only has one screen and I know almost nothing about twinview, sorry. But I fail to see what's wrong with having the two screens merged into a single 2880x900 desktop ? I thought that creating an extended desktop was the whole point of twinview ?