Shares of Agco ( AG) were among the NYSE's losers Friday, falling 7% after the maker and distributor of agricultural equipment slashed its 2006 earnings and revenue forecast. The company sees earnings of $1 a share, with a 2% to 3% revenue decline. Previously, the company said that earnings would grow by about 10% and that revenue would be slightly below 2005 levels. During 2005, the company posted adjusted earnings of $1.46 a share on revenue of $5.4 billion. Analysts polled by Thomson First Call project 2006 earnings of $1.45 a share on revenue of $5.33 billion. Agco blamed the shortfall on its continued effort to reduce dealer inventories, softening market conditions and thinner-than-expected margins. Shares were trading down $1.96 to $24.29. General Motors ( GM) tumbled 5% after Jerry York, an ally of shareholder Kirk Kerkorian, stepped down from the automaker's board. In addition, Kerkorian's firm backed away from plans to buy more GM shares. The move comes after GM ended talks about an alliance with Nissan and Renault, a deal Kerkorian strongly supported. GM shares were down $1.66 to $31.47. Guitar Center ( GTRC) slid 8% after the music retailer cut its third-quarter forecast. The company estimates earnings of $10.6 million to $11.3 million, or 36 cents to 38 cents a share, and revenue of about $473 million. The guidance includes a one-time real estate gain of 4 cents a share. Previously, the company said that it would earn 40 cents to 46 cents a share, before the real estate gain, on revenue of $489 million to $501 million. Analysts project earnings of 42 cents a share on revenue of $487.7 million. "We experienced uneven sales in both our Guitar Center and Musician's Friend divisions," the company said. "Our Guitar Center comparable-store sales were soft in the first two months of the quarter, with trends improving markedly in September." Shares were trading down $3.63 to $42.