Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You wrote a first table, and it has a problem with its ending. A first table lists several conditions with values, and picks the value of the first condition that is true. To keep it complete, the last entry must be an else, and nothing may come after it. This table broke that rule in one of two ways. Either it has no else at all, or it has an entry written after the else. Why does this matter? If there were no else, a moment could come, at run time, when no condition is true, and the table would have nothing to answer. The engine does not want to find that out in the middle of a program. So it makes the question impossible: every table must end with an else, and it is checked at parse. Entries after the else could never be reached anyway, so they are refused too. The message tells you which one you wrote. The fix: add an else with a sensible default value at the end, or move any stray entries above it. Then the table always has an answer.
Text from the Rush engine's error catalogue.