[Zope] rendering a variable defining the name of a Zclass instantiation

I'm defining a variable in a let tag by dynamically creating the name of a Z Class instantiation. When I render the variable in a with tag <dtml-with "_[VariableName]" It throws a KeyError exception in careful_gettime() from DT_Util. If I hard code the same object name, it works just fine. I can't figure out how to render a variable that defines the name of an object that is not part of my DTML method. Any help would be greatly appreciated. Thanks, Chad