I'd say the board mostly has a bit of a problem with Van Gaal, as he can be very controversial. Sort of like Mourinho, except Mourinho always gets away in the media with his bullshit endavours. Van Gaal won't. If its true that Bobby Charlton hates the way Jose behaves, I'd imagine he might also have a problem with manager who is capable of literally walking around the backroom waving his **** at people.
I completely agree that after the bitter season United needs seasoned manager who will be up to the challenge, but for the same reasons it wouldn't hurt if he was also media darling. Which Van Gaal isn't, and Giggs is.