That paper comes from the same group as the original MM paper (one of the authors studied under Mann even), has some of the same problems and was itself rebutted:

https://climateaudit.org/2006/08/30/wahl-and-ammann-again-1/

WA reported that reconstructions without bristlecones (their Scenario 6) lack “skill” in reconstruction and “climatological meaning”, a finding with which we concur. The NAS Panel says that bristlecones should be avoided in temperature reconstructions. Thus, MBH-type reconstructions (with PC networks) with or without bristlecones are both eliminated. So much for the “refutation” of our criticisms.