I have some Primo SGT Euro BMX cranks that are JIS square taper.

http://harriscyclery.net/page.cfm?Pa...ils&sku=CR1307

So, not all BMX cranks are ISO taper.

Just FYI, I have a 122mm BB which gives a low 40'ish chainline with the chainwheel on the inside of the crank arms.

Maybe you can check for defective taper by comparing the left and right side cranks. Are the pedals the same distance from the chainstay on both sides? If the right side is way farther from the chainstay, that might be a clue. It could mean the right side isn't fully seated or maybe you don't have the bottom bracket you think you have. Could it be one of those weird asymetric ones.