Comment 7 for bug 768614

This is actually a bug in package ucf, identical to Debian bug 574266 (https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=574266#18), which was recently fixed with a one-line patch.

The code that tested for terminal availability would fail if the debconf ncurses interface (whiptail) was used, and the program was /not/ run under X. So when upgrading from the console or via ssh (without the -x option), it would always generate this error message,

For additional details, see the Debian bug report, which includes a patch.