I had an incorrect proof in a paper I wrote in Mathematics of Computation; it wasn't noticed until three years later, at which point I wrote another paper in the same journal with a (correct) proof of the result -- with the slight difference that the correct proof was five pages long where the incorrect proof was five lines long.
The reason the result I claimed was not significantly wrong (the correct theorem required the additional assumption that nobody does floating-point arithmetic with less than five bits of precision) was because I discovered the result experimentally: When I was writing the first paper, I needed an error bound and wasn't sure what it should be, so I had my computer do millions of trials on random inputs and tell me the worst rounding error which it encountered. Only after experimentally convincing myself that I had the right result did I try to come up with a proof.
EDIT: I should add that the result in question concerned the maximum rounding error which could result from multiplying complex floating-point values -- so it's not exactly an esoteric problem which nobody would care about.
Would you mind sharing a link to your papers? From scholar.google I'm guessing this is the corrected version but it didn't list anything older. (http://www.daemonology.net/papers/fft.pdf)
The reason the result I claimed was not significantly wrong (the correct theorem required the additional assumption that nobody does floating-point arithmetic with less than five bits of precision) was because I discovered the result experimentally: When I was writing the first paper, I needed an error bound and wasn't sure what it should be, so I had my computer do millions of trials on random inputs and tell me the worst rounding error which it encountered. Only after experimentally convincing myself that I had the right result did I try to come up with a proof.
EDIT: I should add that the result in question concerned the maximum rounding error which could result from multiplying complex floating-point values -- so it's not exactly an esoteric problem which nobody would care about.