Microsoft’s $6.4B acquisition — its second biggest, behind Skype — didn’t turn out quite the way execs envisioned. The software giant hoped that aQuantive would provide a lot of muscle for its efforts to become an Internet ad sales power. It says today that although the acquisition “continues to provide tools for Microsoft’s online advertising efforts,” it “did not accelerate growth to the degree anticipated.” As a result it will take a $6.2B charge which it will attribute to its Online Services Division. The SEC requires companies to write down the value of an acquired asset as soon as it recognizes that it’s worth less than the company paid. Microsoft says that the hit shouldn’t affect its ongoing business. It notes that “Bing search share in the U.S. has been increasing, revenue per search (RPS) has been growing, MSN is the No. 1 portal in 29 markets worldwide and the company’s partnership with Yahoo! has continued to expand geographically.” Wall Street took the announcement in stride. Microsoft shares are down less than 1% in after-hours trading.