This is an odd thing to say the least. It may also have been no mystery at all. I'm going to post it because it comes from an apparently very rare small book in the SITU library, and the "case" shows up neither in Alberto Rosales' Humanoid catalog, nor in UFO-DNA, nor is talked about on the internet, so I think it's essentially a forgotten incident.
It is of course possible that it is appropriate that it is forgotten. Perhaps nothing happened here at all --- there is certainly not much to go on. But this tale is at a minimum interesting; and maybe it might spark some ideas in somebody's head, so here it is.
The story, "The Transparent People", was told to a person named William J. Eisenman by a New Jersey farmer named Frederick von Krueger --- admittedly any illusions nowadays to "Freddy Kruger" are unfortunate, but we will ignore such trivia. The book was written in 1972, and says that the incident occurred "ten years earlier". I always find such casual comment irritating as a researcher, but let's take this literally and say the event happened [or not] in 1962. The tale gets on paper when Eisenman hears about it, and goes and listens to Krueger's narration of it, and mainly repeats the narrative as told with surprisingly little inquiry of the teller to clarify or revisit anything. The result is a very small hardcover book of 27 pages if you include the title and table of contents. I found this well within my scope of reading stamina, though not always my comprehension.
I'm going to try to illustrate this tale out of thin air [so don't take the illustrations overly seriously, but the above one is genuine as it is in the book].
Fred Krueger was a small acreage  farmer in Old Tappan, NJ. One evening, time of year not stated as usual, he was getting ready for bed [c.11:30pm]. He undressed and went right to sleep. His next awareness was that he was standing naked outside of his house in the yard --- no idea how he got there.
He was walking out from the house and past a round metal storage building he had there. He felt that he was walking involuntarily but wasn't resisting it.
Ahead of him he saw what he thought at first was his round building, but then realized that he'd passed it already. Coming closer, he saw it as "two soup bowls inverted one atop the other" with a small dome. And it was landed in his field.
During this time, his wife, who had not gone to bed, heard what she thought were voices outside, but couldn't understand anything said. She searched the house for her husband, and finding the bed empty, assumed that he'd gone outside, possibly talking to someone. She called out, got no answer, no further conversation occurred, and she let it go. [This is one of the ridiculous failings of this book. Mrs. Krueger is the "supporting witness" in the story, but nothing whatever is said about her, whether she was deceased, whether the transcriber talked to her... nothing].
Meanwhile, Krueger found himself standing next to the vehicle and almost on top of a "platform" of softly luminescent "ivory" with various colors swimming within it. Upon stepping onto this platform he was raised into the craft.
Once inside the inner corridor was bathed in a low intensity light. He describes this as something like Ivory, but his words give more the impression of something pearlescent. He wandered a bit down the corridor and entered a room, which contained a gray-colored chair.
He felt compelled to sit in the chair facing what seemed to be a curtain of hanging disks just in front. The chair then moved "into" the soft disk-wall and he found that he merged into it like a mold. Once completely inside the mold, two soft objects fitted over his ears and he fell asleep.
Rather than trying to revisit this part of the episode later, I'll say now that Krueger says nothing more about it --- no speculation. I, however, have no such qualms. This is to me a rather neatly imaginative way of guessing how a human could be placed in a safe stasis for some very unusual travel to 'elsewhere', for at the end of this episode Krueger regains his feeling of self-conscious mobility, leaves the ship, and steps onto a location like-but-not-identical to Earth.
It is at the moment that he jumps off the craft to the ground that he turns and has a fairly good look at two of his "captors". His description is terribly inadequate. All you can divine from his words is that they were humanoid in shape, and looked as if they were made of the same light [pearlescent and somewhat transparent] that he'd experienced everywhere on board.
When Krueger jumped, he floated gently to the ground. This area of the planet was desert and mountain, almost entirely of red sedimentary rock. Scrub bush scattered about and trees ran up hillsides. Above the mountains in the distance was a bluish haze.
Four other of the creatures were standing somewhat near a huge tunnel entrance which was mechanically carved out of the mountain. Krueger hesitated for a long while, but as they were not paying any attention to him, and he currently saw no other option, he entered the tunnel.
The tunnel was extremely long and lighting was dim, coming from somewhere above. Krueger walked along hugging one side, mainly un-met and uneventful.
Finally he came to an offshoot where you could see down at the end a lake of water [all this apparently still inside the mountain]. At the bottom of this side passage, he found a bench by that lake. There he rested and tried to think. There was no sound, no birds, no animals of any kind. Out in the lake there seemed to be a geyser spraying shimmering water, dancing like a thousand glittering mirrors. Krueger felt at peace here. This place, due at least to the dancing geyser, had life; the rest of the planet, the tunnel, the transparent people, seemed like parts of a tomb.
During this time, Krueger saw two separate "people" emerge from doors in the mountain wall and walk right by him. He then saw two of them emerging in a canoe from a dark cave area, cross to an archway out in the lake and disappear behind it. Krueger was puzzled and concerned that these beings apparently didn't care whether he was there or not. He wandered briefly to the lake shore and saw small fish therein. This led to a concern as to whether other more dangerous things might be in there, and he backed away. Ultimately, he decided that even the pleasant lake was a dead end and went back up the tunnel. At the entrance the four beings were still standing about, and still taking no notice of him. They never moved nor spoke. He made his way over to the pearlescent platform and jumped on it. Into the vehicle he went--- no sign of the beings anywhere. He found the room with the chair and the curtain of disks. He sat. The curtain encompassed him... and he slept.
Most irritatingly, it is not stated whether he woke outside in his field naked, or in his bed.
So what was this? Easily the number one hypothesis would be a vivid imaginative and strongly-convincing ambulatory dream. Krueger doesn't seem the type, but we don't know enough about him. Was he fascinated with UFOs or Space or Science Fiction? Eisenman, as usual, has done a lousy job on such things. [The only comment from the UFO community that I've found was from Lou Farish, who suggested that Eisenman and Krueger sit down and start all over with the details]. All we know from the text is that Eisenman himself was interested in all manner of absurd things and that Krueger was an amateur cave explorer once. Krueger, like many UFO experiencers, later became very interested in NASAs work in hopes of finding out something which would help him understand his own encounter. Certainly nothing like profiteering or fame is playing any role here.
But what, or who, is??? Could Frederick Krueger possibly have really gone somewhere beyond the Earth???
Well, it's fun to think about anyway.