Destination Host Unreachable

The great love of the hero's life has died, and the hero simply cannot take the grief. Desperate to have his significant other returned to him, the character delves into things better left unlearned and discovers a way to bring the loved one back.

Unfortunately, something goes horribly wrong.

This rare Sub-Trope of Came Back Wrong occurs when the resurrectee comes back just fine, but due to the logic of death in the story, lands in a different reality/dimension/existence/class/situation and becomes completely or almost completely unreachable to the resurrectionist. To further the tragic effect, the resurrectionist (who may have been indirectly involved in the resurrected one's death) may feel they have to distance themselves from the reanimated character as self-punishment, or as the only means to "let her/him lead the life they deserve."

Depending on whether or not the Love Interest was mutual and/or whether or not the resurrected one knows his/her situation, either the resurrectionist, the resurrectee, or both may suffer lifelong or eternal bereavement. In other words, body and soul come back fine, but the ominous shadow of death is just too strong to be overcome.

The Trope Namer is an Internet error message.

As a Death Trope, Spoilers ahead may be unmarked. Beware.

Examples of Destination Host Unreachable include:

Anime and Manga

At the end of the 2003 anime version of Fullmetal Alchemist, Ed finally gets Al's body back...in exchange for being shunted from Amestris (and erasing all of Al's memories from being a suit of armor) and ends up stranded in another world, forever separated. You just can't win, can you?
- In The Movie, Al regains his memories and is reunited with Ed, but at the cost of being stranded away from Amestris too, not to mention Al's counterpart is killed as well.
Magical Shopping Arcade Abenobashi exhibits this when Eutus tries to resurrect Mune-Mune and Grandpa Masa in their original lives in ancient Japan. The ritual was successful, as they were both resurrected in the “real,” modern-day world, and Eutus can even go there to see them. But Eutus still separates himself from them, realizing if he stayed they would have died in the exact same way.
Due to the way the afterlife works in Bleach, it's pretty much statistically impossible for someone to reunite with loved ones after ascending to the Soul Society.
We're not quite sure how this trope is played in Puella Magi Madoka Magica, but Homura's wish for Madoka to not die during Walpurgis Night has similar effect. Madoka is fine because the universe is rewound to the time before Walpurgis Night, but Homura finds that she turns cold and unreachable due to the inevitability of Walpurgis Night and the Groundhog Day Loop implication of her wish.

Comic Books

In The Ultimates, Ghost Rider returns to life after making a bargain with a demon to continue sending souls to it. His wife is happy now, with a new family and a "great sex life" (as the demon is oh so proud to taunt Ghost Rider with), but he keeps his distance from her, just satisfied to know that she's happy.
In Spawn the title character comes back from the dead, but arrives several years late to find his love has already remarried.

Film

In the curious Jean Cocteau's French film Orphee, the story of Orpheus is changed so that, even after he brings her back from the underworld, Orpheus can still never look at his wife Eurydice or else she'll return to the underworld for good. Needless to say, this doesn't last long.
In The Imaginarium of Doctor Parnassus, the titular doctor loses a bet for his daughter's soul. Distraught over the loss, he makes another deal to get her back by sacrificing the life of a conman. Once his daughter returns, Doctor Parnassus decides to remove himself from her life, rather than continually subject her to his otherworldly gambling addiction.

Literature

Harry Potter and the Deathly Hallows, has the Resurrection Stone, which can bring people back from the dead, but just enough so that they're not dead or technically alive, and suffer while with the living.
- It also seems to depend on the intent of the person using the Stone. Cadmus Peverell, the Stone's original owner, tried to use it to bring back the girl he loved. She suffered, and he committed suicide to be with her properly. When Harry used the Stone to bring back James, Lily, Sirius and Remus, he believed that he was about to die and would be joining them soon. They greeted him warmly, and comforted him.
A Herald from Mercedes Lackey's Valdemar books can choose to return as a Companion; it basically just takes saying pretty-please to the Powers That Be in the Havens. This is kept secret from living Heralds because there's just no way it will end well emotionally. Which would be worse: to know that your beloved spouse/sibling/child has returned to the world but can never be with you, or to wonder why they didn't?
A sort of example in the Ravenloft novels. The vampire lord Count Strahd Von Zarovich has tried various attempts to claim the soul (and reincarnations) of his beloved Tatyana only to fail. Several novels hint that this may well be because only part of Tatyana's soul remains in Ravenloft, the rest is elsewhere on another world.

Live Action TV

in Heroes, Hiro's final attempt to save Charlie. In the end he manages to save her from being killed by Sylar, only to have her immediately kidnapped by another villain and sent to the past. He meets her in the present when she's old and has lived a life separate from him that he can't take away.

Video Games

In Persona 2 Innocent Sin, Maya Amano is stabbed fatally with the Spear of Destiny. Philemon offers to bring her back by creating an alternate reality, at the cost of the party's memories and their friendship. Tatsuya refuses to forget, initiating the events of Eternal Punishment. However, even at the end of this chapter, Maya and Tatsuya must give up their memories of each other to avoid a paradox that would destroy the world.

Web Comics

Sort-of-happens in Gunnerkrigg Court. Anthony Carver sank into despair and then into insanity after his wife died. So he had the bright idea to go find the psychopomps, since he was told she used to be somehow involved with them. Eventually he met some critters from The Realm Of The Dead - of whom we know only that they don't like psychopomps, and it's hard to tell their attitude toward anything else, and he knew nothing. And they told him how to see his wife again. It's impossible to tell how this would turn with a normal human, but Surma was not one, "passed on" differently, and part of her spirit stuck around (specifically, transferred to their daughter). Even if normally the process would work without any side effects beyond what the crazy dabbler did to himself, this time it was bound to go bad, and not just for him.