It sounds like failure of the optical block. Usually it's a pink stripe, but probably just depends which colour chip has the issue. It's to do with the glue they used to make the block with apparently. JVC replaced some people's projectors with newer models because of this, but I think they are now trying to repair them instead. If it's out of warranty, then might be beyond economical repair.
You could always switch on the 2.5% masking to see if this will be enough to hide the stripe, then zoom your projector a little more to fill the screen. You'll lose 2.5% of the image, but if it's out of warranty, then better than nothing I think.