firmware update failure for Lenovo A603

hi guys....how are things? cud someone please help me with my lenovo a606? i am a bit struggling updating its firmware...i have no trouble downloading it OTA but when it comes of installing it...its says /system/priv-app/av68-android-6.8.06.00.apk has unexpected contents...my current firmware is A606_S020_140813_ROW and suppose to be updating to A606_S040_150702_ROW...please guys i need your help....i would be mostly appreciative and sooner perhaps....thanks...