No one is really sure on the real reason. HU said he he had a personal assistant who would set up for him, something none of the other guys had. A mistake was made and he ended costing the band $800 a month. They forced him to lose the assistant. He got mad and didn't show up to the airport for their tour a while later, so Charlie had to sing his parts.
Deuce's story, however, is much different. He says his assistant set up for everyone in the band and they all paid him out of pocket. He said that all he showed up late to the airport and the manager told him the band split up. He also said Johnny had it out for him, which was the main reason both he and Biscuit were kicked out of the band. Johnny wanted more attention and didn't like that Biscuits and Deuce were getting bigger than him.