Even after going to rehab, troubled singer Amy Winehouse can't seem to get her act together. The 27-year-old, who has been plagued by substance abuse issues for much of her career, has canceled a series of European appearances after a disastrous kick-off show on Saturday at Belgrade, Serbia's Forest Fest.

Appearing unsteady on her feet and seemingly drunk -- after reportedly showing up more than an hour late -- Winehouse repeatedly left the stage during the 90-minute performance, seemed to forget the lyrics to many of her songs, dropped the mic, clutched at her stomach and face at points and reached out to hug her bandmates as fans booed the woozy set. To make matters worse, she addressed the disgruntled crowd of 20,000 by saying, "Hello, Athens."

Video of the set shows Winehouse to be glassy-eyed and nervous as catcalls interrupt her erratic vocals during what the local Serbian press described as a "scandal" and a "disaster."

On Sunday, Winehouse canceled planned appearances at festivals in Turkey and Greece. "Despite feeling sure that she wanted to fulfill these commitments, she has agreed with management that she cannot perform to the best of her ability and will return home," her spokesperson explained in a statement. "She would like to apologize to fans expecting to see her at the shows but feels that this is the right thing to do."

The disastrous show came just weeks after Winehouse entered an alcohol rehab program, according to People, and British reports claimed that alcohol had been banned from the 12-date tour.

The singer has reportedly been [article id="1643709"]working on the follow-up[/article] to her Grammy-winning 2006 breakthrough, Back to Black, but no release date has been announced for the disc.