NEW YORK (CNN/Money) - Shares of AOL Time Warner Inc. fell Wednesday as investors worried about the health of the media conglomerate's Internet business.

Shortly before the market closed, AOL (AOL: Research, Estimates) shares had fallen $1.06 to $20.79, a decline of nearly 5 percent, driven in part by analyst comments about recent management changes at the company.

On Tuesday, Barry Schuler stepped down as head of AOL's Internet unit, and the company named Chief Operating Officer-elect Robert Pittman as Schuler's temporary replacement.

"There are some real problems at AOL, primarily around ad sales, and there are some real strengths that people are calling problems,'' Pittman, attending a Fortune magazine conference in Chicago, said.

Wednesday morning, Merrill Lynch analyst Jessica Reif Cohen said the move was a sign that business was worse than expected at the Internet unit, which has struggled to expand its share of the broadband market even as it loses revenue from dial-up customers and suffers through a weak advertising market.

While acknowledging that Pittman, who ran AOL operations before the company merged with Time Warner in 2000, was well-qualified to address these issues, Cohen said management shake-ups have a negative impact on earnings and wondered if Pittman was being spread too thin.

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"Management's ability to address and resolve these items will be the key driver to growth in profitability in the long-term," said Cohen, who maintained a "neutral" rating on the shares.

The selling mood was fueled by word of a sale of more than 18 million shares by an unknown money manager. Reuters reported the large sale, but had no other information.

AOL is the parent company of CNN/Money.

-- Reuters contributed to this report.