NEW YORK (CNN/Money) - Trading of General Motors shares was briefly halted on the New York Stock Exchange Thursday, and fell after trade resumed amid unconfirmed market rumors of accounting irregularities at the world's largest automaker.

CMS Energy stock fell to their lowest level since 1986 as rumors circulated that the Dearborn, Mich.-based utility holding company was considering cutting its dividend.

But IPO stock Hewitt Associates rose sharply in its market debut as investors bet the company will continue to be a leader in the fast-growing human resources outsourcing business.

GM (GM: down $1.58 to $51.50, Research, Estimates). The world's No. 1 automaker denied market rumors that it had any accounting irregularities, and said it is not being investigated for its accounting practice.

CMS Energy (CMS: down $0.54 to $10.46, Research, Estimates). The company, which inflated revenue by $4.4 billion over an 18-month period through questionable power swaps, said Wednesday it is shutting down the "speculative" arm of its energy trading business and anticipating lower earnings this year because of reduced trading activity.

Renaissance Learning (RLRN: down $3.05 to $20.86, Research, Estimates). The maker of educational software forecast second-quarter earnings below Wall Street's consensus estimate and lowered its full-year outlook due to reduced government spending on schools.

Omnicom Group (OMC: down $4.51 to $44.30, Research, Estimates). The world's third-largest ad conglomerate fell after Moody's placed the company's senior unsecured debt on review for possible downgrade Wednesday.

SimpleTech (STEC: down $1.92 to $3.78, Research, Estimates). The maker of products based on memory-chip technologies cut its second-quarter per share forecast Wednesday to a loss and also lowered its revenue forecasts, citing a sharp fall in memory chip prices.

nVidia (NVDA: down $2.99 to $17.08, Research, Estimates). Graphics chipmaker falls after chipmaker Cirrus Logic (CRUS: up $0.68 to $6.79, Research, Estimates) warned of a revenue shortfall from slack production of Microsoft's XBox video game console.

Fresh Del Monte Produce (FDP: down $1.98 to $24.91, Research, Estimates). Morgan Stanley downgraded the stock to "equal-weight" from "overweight," citing current fair valuation and tough third-quarter competition in banana pricing.

RFS Hotel Investors (RFS: down $0.55 to $13.30, Research, Estimates). The travel company lowered its second-quarter earnings outlook, citing continued softness in business travel and short-term dilution from a recent stock offering.

RealNetworks (RNWK: down $0.79 to $3.50, Research, Estimates). The company warned investors it would post a loss for its second quarter because of weaker sales for its digital media delivery software. RealNetworks said it expects a net loss of 1 cent or 2 cents per share for the quarter. Analysts had forecast a profit of 1 cent per share, according to First Call.

Visteon (VC: down $0.84 to $13.64, Research, Estimates). Goldman Sachs downgraded the auto parts supplier to "market perform" from "buy," citing risks associated with automaker Ford's production slowdown. The company on Wednesday raised its second-quarter forecast.

Hewitt Associates (HEW: up $4.50 to $23.50, Research, Estimates). The Lincolnshire, Ill.-based consulting and human resources outsourcing firm is betting that companies will continue to outsource human resources departments, like payroll and retirement benefits, to help reduce costs.

Sun Microsystems (SUNW: up $0.46 to $5.17, Research, Estimates). Goldman Sachs said the maker of high-end servers is showing better-than-expected progress toward its fourth-quarter goals of sequential revenue growth and nominal profitability.

Micron Technology (MU: up $1.50 to $20.50, Research, Estimates); Conexant Systems (CNXT: up $0.38 to $1.47, Research, Estimates). Lehman Brothers upgraded the memory chipmaker to "strong buy" from "buy" and upped its rating on Conexant to "buy" from "market perform," saying their "valuations have started to reach compelling levels."

Corixa (CRXA: up $0.83 to $6.45, Research, Estimates). The pharmaceutical firm and British drugmaker GlaxoSmithKline said the FDA has agreed to a new review of cancer drug Bexxar. The companies said the federal agency granted the appeal to review the regulatory status of Bexxar, which targets non-Hodgkin's lymphoma. The drug is being jointly developed by Corixa and GlaxoSmithKline.

Motorola (MOT: up $0.41 to $14.45, Research, Estimates). The wireless equipment manufacturer announced it is cutting another 7,000 jobs as it takes $3.5 billion in charges to restructure its business and write down the value of some of its assets. The company also reaffirmed its second-quarter and 2002 guidance.

Qwest (Q: up $0.97 to $2.76, Research, Estimates). Shares recovered slightly after falling sharply Wednesday in the wake of the WorldCom scandal and reports the Securities and Exchange Commission is taking a tougher stance on how the company accounted for $1.4 billion in revenue.  

-- from staff and wire reports