When attempting to upgrade PPM from 15.3 to 15.5, the install fails during the check-install part, and the following error is thrown in the logs: (UnknownElement) Task "proputil" finished with error.
To resolve this:
1. Move the check-logs folder and the checkinstall.properties file to a temporary folder
2. Then re-run the checkinstall.bat file
3. Lastly, run the installer which should now complete successfully