[SOLVED] Calling a macro in a filter

I am having a miserable time with Loop Values, trying to do something I thought should be simple.  (The hard parts all work fine  ::) )

I am looping on a single field, which I specify in the Parameters tab of the GUI.  I put in my attribute name, rename the iteration macro to something meaningful and can see the option to parallelize iteration (which tells me I have expert mode turned on and am seeing all the parameters).  The first task inside of the loop is to filter the data on that same attribute, using the iteration macro.  The parameter string I am using is:  

valuefield == %{macroname}

Specifically the XML said:

<operator activated="true" class="filter_examples" compatibility="5.1.015" name="Filter Examples (2)">
 <parameter key="condition_class" value="attribute_value_filter"/>
 <parameter key="parameter_string" value="valuefield == %{macroname}"/>
</operator>

I am getting an error that says that there are no examples in my example set.  There are 3.45MM coming in to the filter, and nothing is coming out.

Is there something wrong with the way I am specifying the macroname?  There are a few values that have extremely small numbers of examples, and the wiki references a parameter (for loop values) called About P that would let me cut those out.  Would that fix this? If so, how do I invoke it?

Rebecca (feeling particularly dumb today)