The Wegman report was made in 2006. It is an independent analysis of the statistics used to create the Hockey Stick, which starred in the IPCC 3rd report. It is here.
The executive summary reports the primary problem with Mann's Hockey Stick paper:
“The controversy of Mann’s methods lies in that the proxies are centered on the mean of the period 1902-1995, rather than on the whole time period. This mean is, thus, actually decentered low, which will cause it to exhibit a larger variance, giving it preference for being selected as the first principal component. The net effect of this decentering using the proxy data in MBH98 and MBH99 is to produce a “hockey stick” shape. Centering the mean is a critical factor in using the principal component methodology properly. It is not clear that Mann and associates realized the error in their methodology at the time of publication.” Finding number 7 discredits claims that the 1990s were the hottest decade in a millennium: “Our committee believes that the assessments that the decade of the 1990s was the hottest decade in a millennium and that 1998 was the hottest year in a millennium cannot be supported by the MBH98/99 analysis. As mentioned earlier in our background section, tree ring proxies are typically calibrated to remove low frequency variations. The cycle of Medieval Warm Period and Little Ice Age that was widely recognized in 1990 has disappeared from the MBH98/99 analyses, thus making possible the hottest decade/hottest year claim. However, the methodology of MBH98/99 suppresses this low frequency information. The paucity of data in the more remote past makes the hottest-in-a-millennium claims essentially unverifiable.” McIntyre and McKitrick exposed the problems and showed that stationary trendless red noise would exhibit the same hockey stick shape after being processed using the MBH methodology! This was confirmed by Wegman.