NEW YORK (MarketWatch) -- One of the first and largest money market funds has put a seven-day freeze on redemptions after the net asset value of its shares fell below $1. Primary Fund rfixx, a $62 billion fund managed by money market fund inventor The Reserve, said Tuesday afternoon that its $785 million holding of Lehman Brothers Holdings debt has been valued at zero. As of 4 p.m., the value of the fund's share is 97 cents. The Reserve said that redemption requests received before 3 p.m. Tuesday will be paid out at $1 a share.