David Einhorn Speaks at Value Investing Congress, Thinks Green Mountain Revenue is Too Good to be True - But is It?

Green Mountain Coffee

is struggling this afternoon after David Einhorn, the legendary hedge fund manager behind Greenlight Capital,

on the coffee maker at the

.

Einhorn has numerous issues with the K-Cup maker, but his biggest complaint surrounds the company's lack of disclosure. According to

, he thinks it's time for the company to become more transparent. Further, Einhorn says that Green Mountain declined to speak to him during what the company claimed was a “quiet period.” Einhorn also noted that the firm has a “looming patent issue” on its single-serve coffees. But Einhorn didn't stop there. He also said that Green Mountain has a “litany of accounting questions” while saying that the company's earnings could be “too good to be true.” This is a huge blow to a company that was making progress with its growing K-Cup brand. Earlier this year, Green Mountain

with Starbucks

and Dunkin' Brands Group

that allows Keurig to sell branded K-Cups at cafes and retailers across the country. At the time of the Starbucks announcement, Peet's Coffee's

. While Bloomberg says that Green Mountain has increased more than 10-fold during the bull market that began on March 9, 2009, the company has watched its stock decline a significant amount today (roughly 11.5% at last check). But Green Mountain isn't the only coffee company that's suffering. Starbucks is down 1.81%, Dunkin' Brands is down 1.67%, and Peet's Coffee is down roughly 2%. Einhorn's assessment may be accurate, but he has had mixed results in 2011. According to Bloomberg, His Greenlight Capital took a modest loss after parting ways with a stake in Yahoo!

. He also failed to successfully acquire a share of the New York Mets. Pfizer Inc.

, Microsoft

, Apple

, and Sprint

are among his

.