I have searched around this site and others and cannot seem to find anyone who has ran into this specific error. Any information could be helpful.
I get the following error when building the Content Wix. The rest of the solution builds just fine, including the Infrastructure Wix and MPS.Content Wix.
heat.exe(0,0): error HEAT5313: Build error during harvesting: C:\WINDOWS\Microsoft.NET\Framework\v4.0.30319\Microsoft.Common.targets(2132,5): The "AssignTargetPath" task failed unexpectedly.
So it turns out that the folder structure was too long in TFS for one of the files used in the web service project which was being referenced in the content WIX.
So I remapped my TFS folder from "C:\Projects\Enterprise\etc..." to "C:\Projects\E\etc..." and that was apparently just enough of a change in folder structure length for it to be able to build.