* Facebook shares volatile in trading debut
* Spanish CDS hit record high, bank shares bounce back
* Winnebago rallies after receiving buyout offer
* Dow up 0.01 pct, S&P up 0.09 pct, Nasdaq flat
By Ryan Vlastelica
NEW YORK, May 18 (Reuters) - U.S. stocks were little changed on Friday, reversing earlier gains after Facebook Inc stumbled in its market debut after a delayed opening.
Shares of the social networking giant were volatile in early trading, falling to near breakeven levels after early gains of more than 10 percent. In early trading it was the Nasdaq's most actively traded stock, with more than 100 million shares traded in the first five minutes of trading.
After a delay in the opening print that drove up anxiety levels among traders and onlookers outside the Nasdaq, the company's closely watched stock began trading at $42.05, compared with an IPO price of $38. It rose as high as $45 before pulling back.
The Nasdaq said it was investigating an issue in delivering trade execution messages from the IPO cross in Facebook.
"We're under a little bit of pressure after this less-than-amazing opening, which is not elevating the market like some had speculated," said Frank Davis, director of sales and trading at LEK Securities in New York.
Shares of companies in the online social media sphere were trading lower. LinkedIn fell 0.6 percent to $104.28 and Groupon Inc fell 5.5 percent to $12.20. Zynga was halted down 13 percent at $7.17.
With the decline, the S&P 500 is on track for a sixth straight day of declines as well as its worst week since the last week of November.
The Dow Jones industrial average was up 0.91 points, or 0.01 percent, at 12,443.40. The Standard & Poor's 500 Index was up 1.18 points, or 0.09 percent, at 1,306.04. The Nasdaq Composite Index was down 0.14 points, or 0.00 percent, at 2,813.55.
The S&P has fallen 6.8 percent so far in May, largely on the back of uncertainty over a political crisis in Greece and whether that could trigger a default and possible exit from the euro zone. While volatility is expected to continue, some analysts were forecasting a near-term rebound as valuations become more attractive.
While much of the market's focus was on Facebook, uncertainties continued to swirl around Europe, and investors remained skittish even as a poll showed Greek voters are returning to the establishment parties that negotiated its bailout.
The cost to insure Spanish government debt against default hit record highs Friday, a day after Moody's cut its ratings on 16 Spanish banks, heightening fears of contagion from the Greek political crisis.
Spanish government-run Bankia shares, up more than 25 percent on the day but still down 31 percent this month, led a rebound in Spanish banking stocks as traders closed short positions. U.S.-traded shares of Banco Santander and BBVA rose more than 4 percent each.
Shares of Foot Locker jumped 10 percent to $30.82 after the athletic footwear retailer posted higher-than-expected quarterly results.
Winnebago Industries Inc surged 5.8 percent to $9 after receiving an unsolicited buyout offer from North Street Capital LP, the investment firm of racing car enthusiast Alex Mascioli, valuing the No.1 U.S. motor homes maker at $321.5 million.