Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You tried to look back in time at a process, and rush told you a process has no stored past. Let's clear that up. The asof token reads old versions of stored data. But a process is not stored data. It is a running thing, a thread of execution, and its life is managed by the engine: it is born, it walks, it ends. Its history is not saved anywhere you can read back, so there is nothing for asof to open. Rush could have handed you the process as it is right now and labeled it the past, but that would be a trick, so it refuses by name instead. Imagine you hold the address of a job in a name, and you ask for that job as of five minutes ago. The question has no honest answer. The fix is in the second slot of the message. If you want history, record what you need from the process into a holder that does keep versions, for example one stored in sulfur, and travel through time there. The process stays a process, and your data keeps its past.
Text from the Rush engine's error catalogue.