Here's a dumb one: My intention was to use the source file GetMetaDataForFile.m in the MetaLinear.codeproj project. Instead, I left the project template's reference to GetMetaDataForFile.c (note the .c suffix) unchanged. The project would try compiling the .c file provided by Apple's importer-project template, and produce a warning that the getter function was not filled. 
 
The sample code disk image that accompanies this site corrects the error.