Jessica Simpson performs at the 99.9 KISS 24th Annual Chili Cook Off at the CB Smith Park, Pembroke Pines, Florida - 25.01.09

The star left fans stunned when she stumbled through her performance at the Van Andel Arena in Great Rapids, mumbling her lyrics, forgetting words and fighting back tears during a 38-minute set, supporting country trio Rascal Flatts.

According to one local concert reviewer, Simpson stopped the show at one point and asked her band to start a song again.

She apologised onstage, by mouthing the word "sorry" to fans, and on Friday (06Feb09), her publicist declared she just had "an off night".

Her rep says, "She's a perfectionist and wanted to start some songs over."

The concert comes as Simpson's apparent weight gain makes headlines in the U.S. tabloids, after the singer was photographed looking bigger at a recent show.

It's not the first time critics have targeted Simpson for her forgetful nature onstage - she was ridiculed after botching Dolly Parton's 9 To 5 hit during a tribute to the country legend at the Kennedy Center in Washington, D.C. in December, 2006.

Source: WENN