Ceea ce ai tu acolo nu e eroare, e doar un avertisment! Functia fscanf returneaza numarul de obiecte citite daca citirea s-a executat cu succes. De aici:
http://www.cplusplus.com/reference/clibrary/cstdio/scanf/On success, the function returns the number of items successfully read. This count can match the expected number of readings or fewer, even zero, if a matching failure happens.
In the case of an input failure before any data could be successfully read, EOF is returned.
Probabil ca tu nu folosesti valoarea returnata de fscanf si atunci iti atrage atentia asupra acestui lucru. Programele ruleaza chiar daca au primit avertismente la compilare, spre deosebire de erori.