Investors weren't impressed Wednesday with Prudential Financial's ( PRU) updated earnings guidance for the coming year. Shares of the New Jersey-based insurer fell 44 cents to $75.34 in afternoon trading, after the company reduced the top end of its 2006 earnings from what Wall Street analysts had been expecting. The insurer says it expects full-year earnings to range between $5.40 and $5.60 a share. Prudential announced the updated earnings guidance in a press release and during an all-day investor conference. Prior to the conference, analysts, as surveyed by Thomson Financial, had Prudential earning anywhere from $5.23 to $5.90 a share. Prudential's earnings estimate, however, assumes a healthy stock market next year. The insurer is banking on an 8% gain in the S&P 500, a move that will increase the value of Prudential's investment portfolio. This year, the S&P 500 is up just 3.6% to date. Bob DeFillippo, a Prudential spokesman, says an 8% gain in the S&P is consistent with the "historical'' appreciation in the index. He says, "historically, that's not so unusual.'' Meanwhile, Prudential also issued earnings guidance for 2005. The insurer said it expects total earnings to range between $4.85 and $4.95 a share. The consensus analyst estimate had the insurer earning $4.97 a share in 2005.