Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You asked rush to write a moment in time as ISO text, and the number you gave cannot be written that way. Let's see what the call expects. Date with the word iso, an a value, and an optional b offset, turns an instant into standard text, like year, month, day, a capital T, hours, minutes, seconds. The instant must be a whole number of milliseconds since the epoch, the start of nineteen seventy. And the standard for this text only has four digits for the year. So the moment, once placed at your chosen offset, must fall between year zero and year nine thousand nine hundred ninety-nine. A value outside that range cannot be spelled. A fraction of a millisecond is not a whole number either. Rush refuses, showing the value and what is wrong, instead of printing a year with five digits that the next reader may not understand. Often the cause is a unit mix-up, like passing microseconds, or nanoseconds, where milliseconds are expected. Divide by the right factor, make it a whole number, and the date will render.
Text from the Rush engine's error catalogue.