I've received both errors over the last couple years using Revit MEP. This error can occur when the supporting files it uses are corrupted somehow. The Factory recommends reinstalling (or using Repair for example) Revit to resolve the issue because this ensures uncorrupted files are installed.
On the other hand if you have access to a working installation you can try the following to resolve the Duct K-Factor error:
On a working PC COPY all the files (to a thumb drive or shared folder) in the ASHRAE folder under Program where Revit is installed. Replace (overwrite) the files that are in the "broken" computer with the "good" files. Try again. This approach using files from a working PC should work. If it doesn't then you'll need to go the repair/reinstall route.
Fwiw, for the Pipe K-Factor error if that occurs you need to replace the PipeKFactors.xml file. It is found in the Program folder (under the installation location for Revit).
The Knowledge Base at Autodesk and the blog post at Revit Clinic attribute the issue to user permissions. While this may be true in some cases it certainly wasn't for me since my computer hasn't changed its permission structure or accounts. Or at least I don't remember doing it...and since I'm the only one using it...hopefully I'd know?