A resolver plugin has a dependency that isn't loading.
The resolver will sometimes display a message when resolving an attribute such as "The PlugIn (foo) is inconsistent. It depends on a PlugIn (bar) that is not registered."
This means you have a data or attribute plugin dependency inside the "foo" definition that isn't working or may not even be found in the resolver file. You need to check the logs more closely for warnings and errors during initialization and check over the file.