if the rebate between the frames are also black i would suspect the film has been exposed to light. If this is sheet film then the edges would exhibit the same problem, in other words, you can't see the edges.
If the rebate shows between frames, it is overexposed, which could be from a variety of factors. Faulty shutter, incorrect metering, etc.
If this is sheet film and the edges are clear then it still reverts back to a shutter or exposurer problem.