Why is Desktop.ini being displayed when logging on to a user?

[acc1]

You have a startup entry somewhere that is pointing to desktop.ini. As ini files default open with notepad it is opening the file. If you download and run a startup editing program like autoruns from sysinternals you can look for the entry and modify/remove it.

http://support.microsoft.com/?id=330132

Many thanks to both Curio and Kane. I can only concur with Rik's comment, well done!

Kane identified the definitive Microsoft article, but it does not say how the problem arose, ie where those pesky desktop.ini files came from.

Microsoft's first suggestion, to delete the offending files, did not work, because the files were in use, presumably by Windows. The second suggestion did work, to use Msconfig.exe and untick the desktop startup entry for each user.