The singer, whose hits include “…Baby One More Time” and “I’m a Slave 4 U,” has been playing a series of shows this summer in Europe, including in Britain, France and Sweden.

The July 24 show in Warsaw was canceled because of a contractual dispute that could not be resolved, a statement released by her publicist said Wednesday.

Phone calls to the concert organizer in Warsaw, Agencja Akwarium, went unanswered. An official Web site devoted to Spears’ Polish stop, said only that the show was canceled and that it would soon post information for ticket holders.

The Warsaw concert was to have been Spears’ second-to-last show in Europe before the “Circus” tour returns to the United States. She is scheduled to play at the 02 Arena in the German capital, Berlin, on July 26.

The 27-year-old “Womanizer” singer is scheduled to embark on an Australian tour in November after performing a series of shows in the U.S. and Canada.