Are you using Windows 8.1 by any chance? If you are using sampling on Windows 8.1, you need to upgrade to VS2012 Update 4 (or a newer version of VS) in order to be able to resolve symbols. This is due to changes in Windows that occurred in the 8.1 release which made it so that the profiler from older versions of VS can't get the unique identifier that allows it to match a symbol file (PDB) with a binary.
More information at my blog post here.
This issue is unrelated to NGEN (which is what the post you linked to is about).