Certification:
http://law.justia.com/us/cfr/title49/49-6.1.2.3.32.html
It may be as simple as how or where the weight labels are located may not be in compliance.
"(d) The label for trailers shall be affixed to a location on the forward half of the left side, such that it is easily readable from outside the vehicle without moving any part of the vehicle."