Calling A Function From A Stored Procedure

Hello all,

I'm trying to construct a select statement in a stored procedure that filters based on the returned values of a number of functions.  My function works fine, but when I try to call the function from the stored procedure I get an error.

I'm going to try explain the thought process behind what I'm doing.  Hope I make enough sense.
The purpose of the stored procedure is to perform a wildcard search on a tool.  The tool contains a number of FK that link to different tables (e.g., manufacturer, vendor).  So I'm creating functions that also search the manufacturer and vendor and return the matching IDs.

Example of tool SELECT statement:SELECT tool_number, tool_description
FROM tool
WHERE tool_manufacturer IN (UDFmanufacturer_SearchName(@search_string)

This gives me an error:
'UDFmanufacturer_SearchName' is not a recognized built-in function name.

Function code (removed some wrapping code for simplicity):SELECT manufacturer_id
FROM manufacturer
WHERE manufacturer_name LIKE '%' + @search_string + '%'These statements both work if I run a independent query: 
SELECT *
FROM UDFmanufacturer_SearchName('mol')
 
 SELECT *
FROM tool
WHERE tool_manufacturer IN (SELECT *FROM UDFmanufacturer_SearchName('mol'))


This code fails:SELECT *
FROM ato_tool
WHERE ato_tool_manufacturer IN (UDFmanufacturer_SearchName('mol'))
 
I'm stuck.  I haven't been able to find anything that shows me where I'm going wrong.  Any thoughts or suggestions are appreciated.
 
Thanks,
Jay