Vista has this nice encryption mechanisms for the whole disk (BitLocker) and single files (EFS), and if you need and use it, then you’d better follow the recommendations. But if you — like me — never ever had a file encrypted on this system and still get strange messages like this you could start wondering. Like I did:

First, check your local drive for encrypted files. They are marked green in the file explorer. Since checking manually is tedious at best, Heinzi pointed me to “cipher /n /u” which lists all encrypted files from the local system. To run that command, open a command line (Win+R -> “cmd”) and type the command without quotes. That’ll take a while, but on my system it didn’t show any files. If you have found any, you should now have an idea where they come from.

In the Management Console (Win+R -> “mmc”), choose “File”/”Add Snap-In” (Ctrl+M) and add the “Certificates” snap-in for your own user. Under “My user account”, “Personal” “Certificates” you can check whether you have any certificates whose intended purpose is “Encrypted File System” and check the creation date (expiration – 100 years). If this doesn’t ring any bells (perhaps that NSA software you installed yesterday?) — mine was already a month old — delete it there. Bye, bye, annoying pop-up!