seems like the function isn't returning anything:
<cffunction name="CheckedBoolean" access="public"
returntype="string">
<cfargument name="rawBoolean" type="numeric" required="true" /
>
<!--- where the cfreturn statement --->
</cffunction >
also, try first renaming your helpers.cfm and creating a new one with
just this method in it. see if something inside your current
helpers.cfm is causing it to be renamed or something.
another thing to try is to just place the method inside your
controller.cfc and see if the method is available to you then.