[Zope] Error calling a Z SQL method

I am calling a Z SQL method from within a DTML method that is called by a DTML document. The Z SQL method is contained within a folder called 'selects'. The error I get is as follows: Error Type: ValueError Error Value: Strings are not allowed as input to the in tag. The following is the syntax I use to call the DTML method from the DTML document: <dtml-call "initialize_parameters(REQUEST, _)"> And, the following is the code I use to call the Z SQL method (i.e. retrieve_data_sql) from within the DTML method (i.e. initialize_parameters): <dtml-in "selects.retrieve_data_sql()"> </dtml-in> I have used this same piece of code in other places without a problem. Any help would be greatly appreciated. Thanks. - Asad