If print film is used, the most likely cause is underprinting by the film processor. If slide film is used, the subject probably covers a small area of the picture. In both cases, the background is both distant from the subject and probably dark. For print film, return the film to the processor and ask that the exposure be made for the subject. For slide film, use the flash auto exposure override or the auto exposure override to reduce (-0.5 to -2.0 or dial or LCD display) the flash output.