Like a red herring, but unintentional.

Will-o'-the-wisp?

http://en.wikipedia.org/wiki/Will-o'-the-wisp

I am not convinced that red herring necessarily implies intention. It is hard to know exactly waht to suggest without knowing the exact nuance that you wish to convey, but you might find something that suits you in the Thesaurus.

http://thesaurus.reference.com/browse/red+herring

How about: "non sequitur"?

From what I've read, a red herring does imply intentional deception, such as in a play, making it seem to the audience that one character is the villain to distract them from figuring out the actual antagonist.

I'll describe the exact situation.

I work in IT. We're creating a wiki page full of these instances of false leads for troubleshooting. For instance, our admin was trying to find the cause of a reported error in his logs because a web service wasn't running. It turns out that the error has always occurred and had nothing to do with the web service. We wrote it down so that it won't happen again.

Since you're looking for an idiom like "wild goose chase," I'd like to advance this suggestion: "wild goose chase."
Also, the Wikipedia version of the origin of red herring is that it's simply bright red and strong smelling which distracts from other dishes, not necessarily intentionally. However, even Wikipedia defines it as being intentional.

Actually, the modern meaning of red herring stems from fox hunting. Farmers who were tired of having the dogs & horses tromp through their fields after a fox would set out pickled red herrings. The scent was so strong that the dogs would lose the fox's scent, & the hunt would hit an impasse.

On topic, I would have to suggest Will O' the Wisp as well. Non Sequitur would also work, but to me it doesn't imply a sense of misdirection that Will O' the Wisp does.

An unintentional red herring. . . . how about a false positive or a faux pas? Led down the garden path? Fell into a rabbit hole? Chasing your tail?

Thank you all for your responses. I'm liking "will o' the wisp" and maybe "chasing your tail."

Rocket, the fox-hunting origin of red herring sounded odd to me (raised in rural hunting territory), and certainly Michael Quinion appears to have debunked it: http://www.worldwidewords.org/articles/herring.htm

Regarding the original question, I presume the intended audience is fluent speakers of English, otherwise such idioms might only serve to confuse. Anyway, I don't see how will-o'-the-wisp fits the bill (a mysteriously floating glowing thing, that will only be a red herring if you try to follow it). False lead may be boring, I think it fits the bill better and is more appropriate for the context. But that's merely my opinion.

The documentation is meant for internal use by fluent (but not always native) English speakers in Southern California.

So far, the page is still called "Red Herrings." Red herring is currently used around the office in this context, but I had reservations about using it in our documentation in that context when I read that it implies intent.

You know, after reading this:
http://www.worldwidewords.org/articles/herring.htm

I feel pretty comfortable using "red herring" to describe unintentional deception. Given its roots--"neither fish, nor flesh, nor good red herring"...meaning something that was nondescript or neither one thing nor another--and its modern accepted usage, I think it works fine for my purposes.

"...and that was his mistake, he was unintentionally led up the garden path" - yeah, it's bit of a cheat, but what they hey!

how about "to be led a merry dance"?