Electronic health record (EHR) systems were initially developed to improve health care delivery by facilitating the healthcare professionals' access to electronically-stored patient information, but problems are regularly reported in the literature. We present here a preliminary study conducted at a 950-bed university hospital. They have implemented an EHR in 2012 to remove their paper-based system. After few years, physicians complain that the EHR is "too complex", "too slow", "unsatisfying", and "which interacts with too many health software". This preliminary study was based on individual interviews inspired from critical incident technique with 9 hospital professionals (physicians and pharmacist) to establish a global diagnostic of the EHR's usability failures/difficulties and their potential impacts. Results show that professionals faced to many constraints impacting their work but more importantly the patient care, with recent outstanding examples. This work is a first step of a larger study to help the hospital to map usability failures, their context of use and associated risks/impacts, and to provide solutions to fix it.