Trigger Error

I have a table:

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CREATE TABLE CATEGORY (
CATEGORY_ID INTEGER IDENTITY(1,1) NOT NULL,
CATEGORY_NAME VARCHAR(40) NOT NULL,
PARENT_CATEGORY_ID INTEGER,
CATEGORY_ICON IMAGE,
DEPTH INTEGER,
CONSTRAINT PK__CATEGORY PRIMARY KEY (CATEGORY_ID)
)
GO

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and i try to create this trigger, but i fail:

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CREATE TRIGGER [AI_CATEGORY] ON [dbo].[CATEGORY]
FOR INSERT
AS
DECLARE @TEMP_ID AS INT, @COUNTER AS INT
UPDATE AI_CATEGORY
SET @TEMP_ID = CATEGORY_ID, @COUNTER = 1
IF PARENT_CATEGORY_ID IS NOT NULL
BEGIN
WHILE@TEMP_ID IS NOT NULL
BEGIN
UPDATE AI_CATEGORY
SET @TEMP_ID = PARENT_CATEGORY_ID,
@COUNTER = @COUNTER + 1
END
END
UPDATE CATEGORY
SET DEPTH = @COUNTER

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And i get the following Error using SQL Server 2000:

Server: Msg 207, Level 16, State 3, Procedure AI_CATEGORY, Line 7
Invalid column name 'PARENT_CATEGORY_ID'.

Any clue?

Coosa