'Build an Approval Process' error

I am trying to complete 'Build an Approval Process, but I keep getting the error : Hi. Please I keep getting an error message : Error: Field Type is a picklist field. Picklist fields are only supported in certain functions. <a href="javascript:openPopupFocusEscapePounds('/HelpAndTrainingDoor?loc=help⌖=tips_on_building_formulas.htm%23picklists_and_msps&section=Customizing', 'Help', 1024, 768, 'width=1024,height=768,resizable=yes,toolbar=yes,status=yes,scrollbars=yes,menubar=yes,directories=no,location=yes,dependant=no', false, false);">Tell me more</a>  

whenever i try to affix entry criteria of Account: Type equals Prospect.