When I say it's broken, I'm not kidding...
Customer has to perform a feature upgrade. The vendor's instructions for said upgrade do not, in fact, actually work. My team has developed our own instructions that more-or-less work (or at least they are not an epic fail.)
For this customer, the administration is outsourced to India to the most incompetent bunch of admins on the planet, the project coordinator is in Brazil, the physical install of the feature upgrade will be done on-site in middle America by a combination of a parts-swapping service tech and a local admin they've hired for the occasion.
I get the call late last week, and immediately give them (the off-shore admins) a list of pre-reqs so the upgrade will actually work. Along with warning them that the upgrade is doomed unless they meet the pre-reqs. I also instruct the level 1 team that if they call in over the weekend, to simply tell them to back out, as I'm not touching this job without the prep work completed.
They (the India admins) naturally fail to pass on this information to the local team (the service tech and the local tech), who finds it out when they read my notes in the support case tracking system. By this point, it's too late to call off the change.
Whaddya know... the upgrade does, in fact, fail. (The new part goes into a reboot loop because it wasn't loaded with code in the factory. This is one of the many known issues with the upgrade; there's a way around it, but it requires prep.)
Now, I get all kinds of flack from the local tech who got caught in the middle. So, the end customer is unhappy, the local tech is unhappy, and the upgrade is still doomed unless the local tech can convince the end customer to let him bill them for the prep work. To top it off, the vendor's local reps insist that the official procedure (the one that didn't work) is just fine, and it must be some particular quirk to this setup.