Internal PhD thesis reviewer pulled out a month before the thesis due date: Is this allowed? What to do next? I have been a PhD student in an institute for the last 4 years and now my deadline to submit my thesis is in another 40 days. When I joined the institute, official papers were signed stating that Professor X will be my first reviewer and will grade my thesis. By regulation, the first reviewer has to belong to the same faculty, but he was not from our group, and we did not have much contact with each other. 

Now that I am ready to submit my thesis, he decides to back out on reasons stating that I was not in touch with him (but I was never told by my supervisor or by him that I need to regularly contact him). 

Does this happen and is this allowed since official University papers were signed 4 years ago saying he will be my first reviewer?
Such situations are not uncommon in academia.  I would caution you against trying to get this person back as a reviewer, even though you have signed papers from 4 years ago.  Simply respect that person's decision to back out, thank her or she for their time thus far, and invest your energies finding somebody that will serve as a reviewer so you can graduate.  Perhaps this sounds like rather odd advice.  Just put yourself in the shoes of a person who doesn't want to serve as a reviewer but is subsequently forced to do so.  You are at risk of getting a very unfavorable review, and the 40 days could become much longer.  You have plenty of time to get somebody on board, and you will certainly encounter situations in your future career that are far more egregious.