You should get in touch with the ministry of education, the university, and perhaps the consulate as well. The problem is, the letter of acceptance (I'm assuming you are a non-EU student) says you have to bring a student visa in order to register. In my case since there is no visa required to enter Romania (I'm from the US which has a visa waiver), the embassy and ministry said I can just give them my passport when I arrive, and I don't need a visa to register. That contradicts the letter of acceptance so I am a little bit nervous, but the embassy said this is what I should do.
In your case, since it sounds like you need a visa to enter the country, I think you might need the student one.. but definitely check