While MTS doesn't have an entry on the original "Thirteen Greatest Error Messages" list (probably a good thing), someone with the screen name EricH posted the following comment in response to the original list:
Does anyone else rememberOf course a $CONTINUE WITH line was never the correct response to this prompt, you could just enter an FDname. But I do agree with the spirit of this comment.
"ENTER LOCATION OF MORE LOADER INPUT, UXREF, CANCEL OR RETURN TO IGNORE?"
This comes from the Michigan Terminal System (MTS) linking loader when it couldn't resolve all the symbols in a program. If you were very lucky you could type something like
$CONTINUE WITH FILE_WITH_MY_LIBRARY
and recover, but generally "CANCEL" was the correct answer.