so ive got a serious problem and im not sure what to do about it.
a while back i put on some FSA vigorelli cranks on my bike with a new fsa platinum pro bb. now after a few miles the bolt that holds the crank onto the bottom bracket spindle loosens and starts to creak. did i do somthing wrong when i installed them? the cranks were used when i bought them but they werent in really bad shape. are these things toast?

I have the same problem!!! I can crank the ***** out of that bolt on the non drive side, until I am afraid of cracking something, and after a few days, it develops some play in it, and I can wiggle it just a tiny bit. it is really disconcerting... I think I need either a new left side crank arm because the hole is not perfectly square anymore, or the BB spindle threading on that side is mussed up.

I had the same problem a few weeks ago With my Miche cranks. I changed my bottom bracket and no more problems..

try some blue locktite on the bolt. If all else fails cut up a coke can and make a shim for the square taper.

SO most likely, if I change my BB ill be ok? Is the blue locktite the one you can get off with some force?

aw man my **** is ISIS should i just get a new BB?

I don't think so. If the crank arm is rounded out, you'll have to replace the arm, most likely both, as they are sold in pairs. It may not be visably rounded. Your situation sounds exactly like one I had a fex years ago. I put on a fancy pair of Curve cranks, made of some kind of soft aluminum. After some hard landings, one of them felt loose. I would retighten it daily, but it would loosen itself each time, getting worse and worse. If however your BB spindle is of a softer material than your cranks, then that's your problem. Rather unlikely however.