Scar tissue and slips
Sometimes you need to have the band unbuckled and the scar tissue under the band removed (lysed). That will give your stomach a break for a bit and a couple of months later have the band re-buckled. In that way you can get back to weight loss.
Vomiting and lapband
If you keep vomiting after the band has been empty, it may have slipped or may be band intolrance. Encourage you to see a bariatric surgeon and have it removed or have pulled it up if yes.
Vomiting with lapband in spite of removal of all fluid
If your Band is too tight even with all the fluid removed, it may have slipped. It really doesn't matter, since the band should be removed no matter what the cause. Ignoring the problem puts you at risk for permanent damage to your esophagus. Don't delay; see a qualified bariatric surgeon and have it removed.