Make sure you have the correct firmware for your version router, the latest fw for v1 and v2 is Ver.1.0.07 (Build 1). For v3 ONLY Ver.3.0.00 (build 6).
Make sure you use the correct firmware, because the v3 fw is much larger (10 MB) and will not fit on v1/v2 router (because it only has 8 MB of flash space)