Uh...
Before you go in and f*ck everything up, I suggest you have a look at the .rej file itself. The parts with minus signs ( - ) are lines that should be replaced or removed, and the parts with plus signs ( + ) are lines that should be added.
When hunk fails it's either because the ' - ' lines couldn't be found NEAR the place they were expected to be (ie, a previous patch or revision added so much code that they are now hundreds of lines lower down the file) OR because those replaced lines couldn't be found AT ALL (ie, they've already been replaced or removed entirely). In the later case, it's much, much, much more difficult - perhaps impossible - to apply your patch.