Error message
In the message, %s marks a value that the engine fills in when it raises the error.
The story
You called data put, the door that adds or updates in one go, and the engine refused. Put expects a holder. A holder is a name bound to a data collection, or to a keyed collection. The very first put into a data holder is what brings its contents into existence. So what went wrong? There are two situations. In the first, the name holds nothing at all. The engine will not invent a brand new holder for you, because if it did, a single typo in a table name would silently create a new table, and you would lose hours finding out why your data went missing. In the second, the name holds something, but not a holder, a number, or a piece of text for instance. The engine will not overwrite it either. The message shows you the name, and then the reason. The fix: check the spelling of the name, and make sure it is bound to a collection before you put into it. A strict door at the front saves a lot of confusion at the back.
Text from the Rush engine's error catalogue.