It sure would be nice if I could get some non-cryptic error text.
Win7 x64, two Windows accounts, both in the Administrator group, and two SE accounts, both with beta access. My Windows account can run the updater and game fine. The other account gets this error. I've explicitly put the other account as having Full Control on the entire FFXIV beta folder. I'm betting the issue is something to do with where to downloader is trying to write files to in order to validate that the current version is up-to-date but I haven't checked that yet.
Has anyone had to jump through specific hoops to get multiple users on the same PC to be able to run the beta?
Oh, and in case it's not clear, I have not modified my installation in any way. I ran uTorrent for the initial mega-download, but I've only used the official patcher since then. I have not made the hardware mouse modification and I'm not running the windower.
My Windows account runs the game fine. The other account does not.