This is a common error and a difficult to debug issue. There used to be an article in the old wiki about it but that wiki is now gone.
What happens is this. Without the quotes, the tablename is not correcly resolved and so defaults to the current table. When you add the load statement, you change the current table to a table that did not contain field "page".
I started to write a bug report and then realized this is not a bug, although it could probably use some clarification. It's legal to use a fieldname to reference the tablename, in which case you would not quote. For example: