[XCNuse]

check your smoothing groups; clear them all and that should solve the problem (or do it quickly without messing anything [if you are using smoothing groups] is to go down the modifier list and select smooth, and check the box so it smooths it and go down to 0.0, and there should be no smoothing.. and that should solve where the error is comming from)

and then go from there to solve what value of smoothing is making it dark like that (i assure you though that that is what is causing it is smoothing groups)