ISIC and Access Rights
The chip in your ISIC card will give you access to a number of rooms (FI classrooms, the PC Room, university study rooms), FI and MU printers (usually available in study rooms; please note you will first need to put money into your SUPO account), as well as to pay for meals in the university cafeteria.
If you fail to open a door you usually open with your ISIC card, it is possible someone has locked it physically with a key. In such a case, ask about the reason at the Reception Desk or ask the Building Administration Department to open the door for you.