AceShowbiz - Whitney Houston's troubled tour has derailed yet again - hundreds of fans walked out of a show in Denmark over her faltering voice. The R&B star's highly-anticipated comeback trek has been blighted by poor reviews and criticism from some fans that her vocals are too weak to carry the show.

She scrapped a string of European concerts in April after she was hospitalized with nose and throat problems, and was later booed by an audience in Birmingham, England because her singing was off-key. Now she is facing renewed concerns for her health after hordes of fans in Copenhagen left her show midway through, complaining about Houston's poor performance.

She then reportedly turned on a section of the audience when some fans began booing as she made a speech paying tribute to Michael Jackson. According to the Copenhagen Post, critics from "all of the major media outlets" in the country slammed the concert, insisting Houston's vocals were weak and tuneless.

Critic Thomas Soie Hansen, of the Berlingske Tidende newspaper, writes: "She looked and sounded like a person who doesn't have many years left to live. At the end of the show she looked like she was ready to explode."