Drop User error in SQL 2005

I am trying to drop a user in SQL 2005 with the following script.

USE [CentrePointSoftware]
GO
/****** Object:  User [MASTER]    Script Date: 10/04/2007 16:24:56 ******/
IF  EXISTS (SELECT * FROM sys.database_principals WHERE name = N'MASTER')
DROP USER [MASTER]

I receive error:
Msg 15138, Level 16, State 1, Line 1
The database principal owns a fulltext catalog in the database, and cannot be dropped.

Any help please