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Hedge fund honcho William Ackman fired off another set of questions directed at Herbalife Ltd. (NYSE: HLF) in yet another move to back up his contention that the nutrition and weight-loss company is a pyramid scheme. But Ackman now appears to be a lone voice from the wilderness.

The Wall Street Journal cites a fund manager who said, “Herbalife stock is becoming immune to Ackman’s bad medicine.” After a tumble of nearly 40% when Ackman first laid out his charges in December, Herbalife’s shares have gained back virtually the entire loss before sliding by about $10 a share again. And even that has turned around in the last couple of days.

Analysts at Zack’s have called this “the mother of all short squeezes,” and there is certainly a large dose of truth in that statement. Ackman appears to have failed to convince investors that Herbalife is indeed a pyramid scheme, and the only reasonable chance he has to win the battle is to force the Federal Trade Commission (FTC) to launch an investigation into Herbalife’s business practices.

The FTC has so far not indicated any intention to investigate Herbalife, but Ackman won’t give up easily. A disclosure by Herbalife that the top 17% of its more than 490,000 distributors earn an average of less than $4,500, excluding expenses and money earned from sales to others, and that the top 194 distributors earn an average of $724,300 each is evidence — to Ackman — that Herbalife’s earlier compensation statements were inadequate. Ackman also wants to know if the company will refund losses to distributors who were misled.

Herbalife’s shares are up about 3.5% today at $37.04 in a 52-week range of $24.24 to $73.00.