From [HERE] Holland's Black soccer players show up to Euro 2012. They are greeted with monkey chants. After their coach complains, he is told that he somehow misheard said chants:

The problems occurred as the players began the session by jogging a lap of the pitch only to be greeted at one end of the stadium with monkey noises and loud jeers. On the second circuit, they were even louder and it was then the players decided not to go around again. "At least now we know what we can encounter," the Holland coach, Bert van Marwijk, said with heavy cynicism. "Very atmospheric." 

Uefa subsequently tried to deny that it was racially motivated, saying they had checked with the Dutch squad and had been told it was not thought to be of that nature. Instead, the official line is that a small part of the crowd was protesting about the fact that Krakow had not been made one of the host cities. 

Another theory that has been put forward is that Wisla's supporters did not want their stadium being used by anyone but their own club and were simply booing the Dutch players. Van Bommel, however, responded angrily when it was put to him not everyone had heard monkey noises. 

"You need to open your ears," he said. "If you did hear it, and don't want to hear it, that is even worse."

Uefa later tried to save face by claiming that there were "some isolated incidents of racist chanting." It's amazing to me that the Uefa officials pretty much did what you see people do here when confronted with charges of racism--deny it actually happened, and then minimize when forced into acknowledgement.