Problem with DLL in release mode

Hi, i'm building a DLL that works fine in Debug mode, but in Release mode doesn´t. I'm opening a PE-File with fopen and reading the first two bytes. In debug mode it read 0x5A4D, but in release i'm getting 0!! And this happen with any position inside the file.
Tnx

change the name of dll in release mode
the names in both debug and relaese mode should be different

C is my favorite language