What went wrong that caused the French never to acknowledge that the Vietminh had moved beyond a "barefoot army" to an organized and directed fighting force?
Two things went wrong to cause this mistake on the part of the French.
First, the Vietnamese started the conflict as a "barefoot army." They only progressed to something more organized after China became communist. The French failed to note the difference as it is sometimes hard to change in the middle of a war.
Second, the French consistently underestimated the Vietnamese. These were their colonial subjects and they had little respect for them. They did not take them seriously enough and were therefore slow to realize that the Vietminh really could change and become a serious threat.