Looks like your old IAP version is a slight typo, should be 6.1.3.4-3.1.0.0_35320 correct?
If so, the runs we did in our lab worked out, so next steps to try:
1. possible firmware file corruption
-try downloading the image again from the support website
-delete the current entry from AMP's firmware page (Device Setup -> Firmware Files)
-upload the newly downloaded image
-attempt the firmware upgrade once again
2. if it still doesn't work after trying the process again, verify settings
-are the IAPs and VC in monitor or managed mode?
-if monitor mode, is AMP Setup -> allow firmware upgrade in monitor mode allowed?
3. if the settings are good, a support case should be opened for our support engineers to assist further.