Four ex-employees at the National Exhibition Centre's Metropole Hotel and a Birmingham booking agent admitted taking part in a £250,000 booking scam.
They took advantage of the conference booking system to divert bogus commissions, normally paid on bookings made by an agent, when firms booked direct with the hotel.
Justin Clark-Vine (33) of Tamworth Road, Amington; Rachel Clarke (28) of Frankton Close, Solihull; John Flynn (21) of Marlborough Road, Castle Bromwich; and Joseph Hockridge (36) of Emerson Avenue, Middlesbrough, all pleaded guilty to conspiring to defraud the Metropole Hotel.
A fifth defendant - booking agent Richard Palmer (42) of Arena Productions, Morville Street, Birmingham - also pleaded guilty to conspiring to defraud the Metropole.
The charge says that between January 1997 and August 2003 they created companies which were used as genuine booking agents when the defendants had set them up to receive fraudulent commission payments.
Two other ex-employees - Robert Lyne (53) of Stratford Road, Wootton Wawen, and John Kreft (44) of Linden Road, Bournville - denied the conspiracy to defraud charge and the case against them was adjourned for trial. The five who pleaded guilty will not be sentenced until after the trail.