I was able to circumvent the error by pressing Ctrl-Alt-F1 and then Ctrl-Alt-F7, which brought me to a graphical screen with the LUKS password prompt.
Then, installation of Nvidia proprietary drivers seems to change the boot sequence so that it falls back to usable text mode on my ThinkPad T61p.
I was able to circumvent the error by pressing Ctrl-Alt-F1 and then Ctrl-Alt-F7, which brought me to a graphical screen with the LUKS password prompt.
Then, installation of Nvidia proprietary drivers seems to change the boot sequence so that it falls back to usable text mode on my ThinkPad T61p.