The prompt means that the criteria is unknown. If you have [Enter a name here] that's what the prompt will say, which is probably obvious to you as you intend to provide it. If you think that you've provided it (e.g. form field reference) and you get prompted, it still means it's unknown. Sometimes it's due to
- a spelling mistake in the criteria (such as in the name of the form or name of the control)
- the hierarchy of the reference to the form field is not correct; perhaps because control is on a subform
- the form is closed
- anything else one can think of that stumps Access when it tries to resolve what you've entered as criteria.